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  • 1.
    Al-Askary, Omar
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Rizvi, Umar H.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Khormuji, Majid N.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Rate adaptive generalized concatenated codes for wireless communication2005In: Proceedings of the INMIC 2005: 9th International Multitopic Conference - Proceedings, 2005, p. 137-142Conference paper (Refereed)
    Abstract [en]

    This paper presents the construction and performance of rate adaptive generalized concatenated codes (GCCs) (sic) on linear block codes over Rayleigh fading Multi Input (sic) Output (MIMO) communication channels with N transmit (sic) N receive antennas. The code design criteria is chosen (sic) that it tries to follow the Shannon capacity of the MIMO (sic). It is envisaged that such codes provide a superior performance over systems that use Maximum Ratio Combining (sic) while maintaining the encoder/decoder complexity within acceptable level of practical usage. Furthermore it is expected (sic) these codes will provide good performance without an interver/deinterleaver because of their good burst error correction (sic).

  • 2. Emadi, M. J.
    et al.
    Khormuji, Majid Nasiri
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Aref, M. R.
    Multi-layer Gelfand-Pinsker strategies for the generalized multiple-access channel2013In: 2013 Iran Workshop on Communication and Information Theory, IWCIT 2013, 2013, p. 6555750-Conference paper (Refereed)
    Abstract [en]

    We study a two-user state-dependent generalized multiple-access channel (GMAC) with correlated states. It is assumed that each encoder noncausally knows partial channel state information. We develop an achievable rate region by employing rate-splitting, block Markov encoding, Gelfand-Pinsker multicoding, superposition coding and jointly typical decoding. In the proposed scheme, the encoders use a partial decoding strategy to collaborate in the next block, and the receiver uses a backward decoding strategy with a joint unique decoding at each stage. Our achievable rate region includes several previously known rate regions proposed in the literature for different scenarios of multiple-access and relay channels. We finally consider a Gaussian GMAC with an additive interference which is known noncausally at both of the encoders and construct a multi-layer Costa precoding scheme that removes completely the effect of the interference.

  • 3. Emadi, M. J.
    et al.
    Nasiri Khormuji, Majid
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Aref, M. R.
    On the achievable rate region of a state-dependent MAC with cooperating encoders2012In: 2012 Swedish Communication Technologies Workshop, Swe-CTW 2012, IEEE , 2012, p. 48-52Conference paper (Refereed)
    Abstract [en]

    The two-user discrete memoryless state-dependent multiple-access channel with cooperating encoders is considered. It is assumed that the channel is controlled with two independent states such that each of the channel state information is noncausally available at one encoder. Moreover, based on the intrinsic characteristic of wireless networks, it is assumed that each encoder strictly causally receive a noisy version of the transmitted signal of the other encoder. Hence, the encoders can cooperate in transmitting the message to the receiver. An achievable rate region for the channel is derived by use of rate splitting, block Markov encoding and Gelfand-Pinsker multilevel encoding along with partial decoding at the encoders and backward decoding at the receiver. Finally, for a Gaussian channel model the proposed achievable rate region is evaluated and discussed.

  • 4. Emadi, Mohammad Javad
    et al.
    Khormuji, Majid Nasiri
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Aref, Mohammad Reza
    Multi-layer Gelfand-Pinsker strategies for the generalised multiple-access channel2014In: IET Communications, ISSN 1751-8628, Vol. 8, no 8, p. 1296-1308Article in journal (Refereed)
    Abstract [en]

    The authors study a two-user state-dependent generalised multiple-access channel (GMAC) with correlated states. It is assumed that each encoder has non-causal' access to channel state information (CSI). They develop an achievable rate region by employing rate-splitting, block Markov encoding, Gelfand-Pinsker multicoding, superposition coding and joint typicality decoding. In the proposed scheme, the encoders use a partial decoding strategy to collaborate in the next block, and the receiver uses a backward decoding strategy with joint unique decoding at each stage. The author's achievable rate region includes several previously known regions proposed in the literature for different scenarios of multiple-access and relay channels. Then, they consider two Gaussian GMACs with additive interference. In the first model, they assume that the interference is known non-causally at both of the encoders and construct a multi-layer Costa precoding scheme that removes completely' the effect of the interference. In the second model, they consider a doubly dirty Gaussian GMAC in which each of interferences is known non-causally only at one encoder. They derive an inner bound and analyse the achievable rate region for the latter model and interestingly prove that if one of the encoders knows the full CSI, there exists an achievable rate region which is independent' of the power of interference.

  • 5.
    Farhadi, Hamed
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Nasiri Khormuji, Majid
    Wang, Chao
    Tongji University, P.R. China.
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Ergodic interference alignment with noisy channel state information2013In: 2013 IEEE International Symposium on Information Theory Proceedings (ISIT), IEEE conference proceedings, 2013, p. 584-588Conference paper (Refereed)
    Abstract [en]

    We investigate the multi-user time-varying Gaussian interference channel (IC) in which each source desires to communicate to an intended destination. For the ergodic time-varying IC with global perfect CSI at all terminals, it is known that with an interference alignment technique each source-destinationpair can communicate at half of the interference-free achievable rate. In practice, the channel gains are estimated by transmitting known pilot symbols from the sources, and the channel estimation procedure is hence prone to errors. In this paper, we model the channel estimation error at the destinations by an independent additive Gaussian noise and study the behavior of the ergodic interference alignment scheme with the global noisy CSI at all terminals. Toward this end, we present a closed-form innerbound on the achievable rate region by which we conclude that the achievable degrees of freedom with global perfect CSI is preserved, if the variance of channel estimation error is proportional to the inverse of the transmitted power.

  • 6.
    Khormuji, Majid N.
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Rizvi, Umar H.
    Janssen, Gerard J. M.
    Ben Slimane, Slimane
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Rotation optimization for MPSK/MQAM signal constellations over rayleigh fading channels2006In: 2006 10th IEEE Singapore International Conference on Communication Systems, Vols 1 and 2, 2006, p. 671-675Conference paper (Refereed)
    Abstract [en]

    The performance of uncoded phase-shift-keying (PSK) and quadrature amplitude modulation (QAM) schemes over fading channels can be improved by using coded modulation techniques. Improvement is due to the coding gain coupled with interleaving and depends on the complexity of the code. Recently, it was shown that constellation rotation coupled with interleaving can be used to improve the performance of QPSK modulation over block-fading single-input-single-output (SISO) wireless communication channels. This paper considers the use of such a scheme with higher order constellation sets such as 8PSK and 16QAM. A framework is then presented for the calculation of the optimum rotation angle for MPSK/MQAM schemes. A simple cost function based on the union bound of the symbol error probability (SEP) is defined. The optimum rotation angle is then found by minimizing the cost function using the gradient search algorithm. The obtained simulation results show considerable improvement over the conventional unrotated system.

  • 7.
    Khormuji, Majid N.
    et al.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Communication Theory.
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Communication Theory.
    Instantaneous Forwarding Strategies for Relay Channels with Known Interference2009In: ITW: 2009 IEEE INFORMATION THEORY WORKSHOP ON NETWORKING AND INFORMATION THEORY  , NEW YORK: IEEE , 2009, p. 42-46Conference paper (Refereed)
    Abstract [en]

    We consider a Gaussian relay channel, with the source and relay operating in different frequency bands. Hence, the received signals at the destination are orthogonal. We also assume that the source reuses the frequency band in which the relay is operating, to communicate with another destination. This results in a scenario that can be modeled in such a way that the relay-destination link suffers from an additive interference which is non-causally known at the source. We present different achievable rates for this model, focusing on instantaneous relaying, i.e., the relay output depends solely on the current received signal at the relay. The main conclusion of our work is that to achieve high rates, one should resort to joint design of precoding with non-linear relaying.

  • 8.
    Khormuji, Majid N.
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Noisy network coding approach to the relay channel with a random state2011In: 2011 45th Annual Conference on Information Sciences and Systems, CISS 2011, 2011, p. 1-5Conference paper (Refereed)
    Abstract [en]

    We consider the three-node relay channel with a random state. We assume that noncausal knowledge of the random state is partially known at the nodes. We present an achievable rate based on the noisy network coding (NNC) and the Gelfand-Pinsker random binning strategies. We then compare the achievable rate of NNC with that of compress-and-forward.

  • 9.
    Khormuji, Majid N.
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    The Relay Channel with Partial Causal State Information2008In: 2008 International Symposium on Information Theory and its Applications, ISITA2008, NEW YORK: IEEE , 2008, p. 1392-1397Conference paper (Refereed)
    Abstract [en]

    We investigate the relay channel with a random parameter whose causal knowledge is available partially at the source, the relay and the destination. We define four different classes of this scenario and establish lower and upper bounds on the resulting capacity. We also show that the bounds axe tight in some cases.

  • 10.
    Khormuji, Majid N.
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Two-Hop Transmission with Second-Hop Channel State Information2008In: 2008 INTERNATIONAL SYMPOSIUM ON INFORMATION THEORY AND ITS APPLICATIONS, VOLS 1-3, NEW YORK: IEEE , 2008, p. 678-682Conference paper (Refereed)
    Abstract [en]

    We consider a two-hop relay channel with a random parameter in the second hop. We present two main strategies for the case when the random parameter is known non-casually at the source. We then introduce the Gaussian two-hop channel with known interference as one instance of the general model, and present achievable-rate results.

  • 11.
    Khormuji, Majid Nasiri
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    On the capacity of molecular communication over the AIGN channel2011In: 2011 45th Annual Conference on Information Sciences and Systems, CISS 2011, 2011, p. 5766248-Conference paper (Refereed)
    Abstract [en]

    We study a memoryless molecular communication channel with an additive inverse Gaussian noise (AIGN). We assume that information are encoded in the release time of molecules and the arrival time of the transmitted molecules at the receiver is the release time plus a propagation delay. Motivated by the Brownian motion, the propagation delay is modelled as an inverse Gaussian random variable. Lower- and upper bounds on the capacity are presented. In particular, we develop simple capacity expressions for cases either when the molecules have a high drift velocity or when the medium has a low diffusion coefficient.

  • 12.
    Khormuji, Majid Nasiri
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Symmetric Capacity of the Gaussian Two-Way Relay Channel to Within 1/4e [nat]2013In: 2013 Information Theory And Applications Workshop (ITA), New York: IEEE , 2013, p. 278-282Conference paper (Refereed)
    Abstract [en]

    The problem of reliable communication over the Gaussian two-way relay channel is considered and a new achievable rate region by combining structured lattice-and random Gaussian codes is presented. It is then demonstrated that the new bound can outperform previously known rate regions. In particular, having found the optimal time-sharing and power allocation policies, it is established that the proposed strategy achieves the symmetric capacity to within 1/4e approximate to 0.092 [nat] approximate to 0.133 [bit], which improves on earlier bounds.

  • 13.
    Khormuji, Majid Nasiri
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    El Gamal, Abbas
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    State-Dependent Relay Channel: Achievable Rate and Capacity of a Semideterministic Class2013In: IEEE Transactions on Information Theory, ISSN 0018-9448, E-ISSN 1557-9654, Vol. 59, no 5, p. 2629-2638Article in journal (Refereed)
    Abstract [en]

    This paper considers the problem of communicating over a relay channel with state when noncausal state information is partially available at the nodes. We first establish a lower bound on the achievable rates based on noisy network coding and Gelfand-Pinsker coding, and show that it provides an alternative characterization of a previously known bound. We then introduce the class of state-decoupled relay channels and show that our lower bound is tight for a subclass of semideterministic channels. We also compute the capacity for two specific examples of this subclass-a channel with multiplicative binary fading and a channel with additive Gaussian interference. These examples are not special cases of previous classes of semideterministic relay channels with known capacity.

  • 14.
    Khormuji, Majid Nasiri
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Larsson, Erik G.
    Finite-SNR Analysis and Optimization of Decode-and-Forward Relaying Over Slow-Fading Channels2009In: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 58, no 8, p. 4292-4305Article in journal (Refereed)
    Abstract [en]

    We provide analytical results on the finite signal-to-noise ratio (SNR) outage performance of packet-based decode-and-forward relaying over a quasi-static fading channel, with different types of transmitter channel state information (CSI). At the relay, we consider repetition coding (RC) and parallel coding (PC). At the destination, we consider receivers based on selection combining (SC), code combining (CC), and maximum-ratio combining (MRC) (the latter only for the case of RC at the relay). Based on available CSI, we optimize the number of channel uses consumed by the source and by the relay for each packet. In doing so, we consider three different protocols that make use of different combinations of long-term CSI, 1-bit CSI, and complete CSI, respectively, at the source node. Several interesting observations emerge. For example, we show that for high SNRs, SC and CC provide the same outage probabilities when the source has perfect CSI.

  • 15.
    Khormuji, Majid Nasiri
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Larsson, Erik G.
    Rate-optimized constellation rearrangement for the relay channel2008In: IEEE Communications Letters, ISSN 1089-7798, E-ISSN 1558-2558, Vol. 12, no 9, p. 618-620Article in journal (Refereed)
    Abstract [en]

    We study the. instantaneous relay channel where the relay's output only depends on the current received signal at the relay. We propose a novel forwarding strategy for this class of relay channels which can outperform amplify-and-forward, detect-and-forward and estimate-and-forward. The proposed scheme is based on a remapping of the signal constellation at the relay.

  • 16.
    Khormuji, Majid Nasiri
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Capacity achieving instantaneous relaying2011In: Wireless Communication Systems (ISWCS), 2011 8th International Symposium on, IEEE , 2011, p. 814-818Conference paper (Refereed)
    Abstract [en]

    A class of semi-deterministic relay channels is introduced and it is shown that for channels in the class capacity can be achieved using an instantaneous relaying scheme. Applications to Gaussian channels are then discussed.

  • 17.
    Khormuji, Majid Nasiri
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Capacity of Two Semideterministic Classes of Multiple-Access Relay Channels2012In: IEEE Communications Letters, ISSN 1089-7798, E-ISSN 1558-2558, Vol. 16, no 10, p. 1529-1531Article in journal (Refereed)
    Abstract [en]

    We investigate memoryless multiple-access relay channels (MARCs) and establish the capacity of two semideterministic classes of such channels: MARCs with orthogonal receive components and state-decoupled MARCs. For both cases, the achievability and converse are proved using the noisy network coding lower bound and the cutset upper bound, respectively. Finally, the capacity of a MARC with additive Gaussian interference is quantified.

  • 18.
    Khormuji, Majid Nasiri
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Hybrid Digital-Analog Noisy Network Coding2011In: 2011 International Symposium on Network Coding, NETCOD 2011 - Proceedings, 2011, p. 5979088-Conference paper (Refereed)
    Abstract [en]

    We investigate noisy network coding strategies for the two-way Gaussian relay channel. We present three hybrid digital-analog noisy network coding schemes. The schemes are constructed by combination of linear analog noisy network coding, Wyner-Ziv- based compress-and-forward, and noisy network coding as proposed by Lim et al. We show that our proposed schemes outperform existing protocols for this problem.

  • 19.
    Khormuji, Majid Nasiri
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Noisy analog network coding for the two-way relay channel2011In: Information Theory Proceedings (ISIT), 2011 IEEE International Symposium on, 2011, p. 2065-2069Conference paper (Refereed)
    Abstract [en]

    An achievable rate region based on Shannon’s inner bound is given for the two-way relay channel. The relaying scheme operates on noisy received signals and generates new analog values to be transmitted to a destination. The scheme is therefore referred to as noisy analog network coding. The achievable rates are then optimized for a Gaussian two-way relay channel, when the relay is memoryless (this type of relaying is also known as instantaneous relaying). For one particular instance of the channel when the received signal at the relay is noiseless, it is shown that instantaneous noisy analog network coding can be optimal. For the noisy case, a numerical optimization algorithm is presented in order to optimize the instantaneous coding strategy. The optimized analog mapping turns out to be nonlinear and periodic. Finally, it is demonstrated that the achievable rates associated with optimized mappings can outperform those achieved by linear relaying, compress-and-forward, and can operate close to the recently proposed noisy network coding scheme.

  • 20.
    Khormuji, Majid Nasiri
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    On Cooperative Downlink Transmission with Frequency Reuse2009In: IEEE International Symposium on Information Theory - Proceedings, NEW YORK: IEEE , 2009, p. 849-853Conference paper (Refereed)
    Abstract [en]

    We study a three-node Gaussian relay channel with interference which is non-causally known at the source. It is assumed that the interference affects only the relay destination link. This model is motivated by a downlink scenario, where the source (base station), communicates with two destinations. We present several transmission strategies for this class of relay channels. Our proposed relaying schemes can be divided into two main categories: instantaneous relaying and causal relaying. In the former, the relay functionality is restricted to a memoryless, symbol-by-symbol mapping (linear as well as non-linear). While in the latter, the relay has an infinite memory and utilizes past received blocks to cooperate in the present block. For causal relaying, we investigate decode-and-forward (DF), compress-and-forward (CF), and combined DF and CF. To utilize the knowledge of the interference at the source, superposition coding at the source and Costa encoding at the relay are employed. One interesting observation is that instantaneous relaying can achieve higher rates than those achieved with causal relaying.

  • 21.
    Khormuji, Majid Nasiri
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    On Instantaneous Relaying2010In: IEEE Transactions on Information Theory, ISSN 0018-9448, E-ISSN 1557-9654, Vol. 56, no 7, p. 3378-3394Article in journal (Refereed)
    Abstract [en]

    The Gaussian, three-node relay channel with orthogonal receive components (i.e., the transmitted signals from the source and the relay do not interfere with each other) is investigated. For such channels, linear relaying is a suboptimal strategy in general. This is because a linear scheme merely repeats the received noisy signal and does not utilize the available degrees of freedom efficiently. At this background, nonlinear, symbol-wise (as opposed to block-wise) relaying strategies are developed to compensate for the shortcomings of the linear strategy. Optimal strategies are presented for two special cases of the general scenario, and it is shown that memoryless relaying can achieve the capacity. Furthermore, for the general Gaussian relay channel, a parametric piecewise linear (PL) mapping is proposed and analyzed. The achievable rates obtained by the PL mapping are computed numerically and optimized for a certain number of design parameters. It is concluded that optimized PL relaying always outperforms conventional instantaneous linear relaying (amplify-and-forward). It is also illustrated that the proposed PL relaying scheme can improve on sophisticated block Markov encoding (i.e., decode-and-forward) when the source-relay link is ill-conditioned (relative to other links). Furthermore, PL relaying can work at rates close to those achieved by side-information encoding (i.e., compress-and-forward), but at a much lower complexity.

  • 22.
    Najari Moghadam, Nima
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Farhadi, Hamed
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Zetterberg, Per
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Nasiri Khormuji, Majid
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Interference Alignment — Practical Challenges and Test-bed Implementation2014In: Contemporary Issues in Wireless Communications / [ed] Dr. Mutamed Khatib, INTECH, 2014, p. 51-77Chapter in book (Refereed)
    Abstract [en]

    Data traffic over wireless communication networks has experienced a tremendous growth in the last decade, and it is predicted to exponentially increase in the next decades. Enabling future wireless networks to fulfill this expectation is a challenging task both due to the scarcity of radio resources (e.g. spectrum and energy), and also the inherent characteristics of the wireless transmission medium. Wireless transmission is in general subject to two phenomena: fading and interference. The elegant interference alignment concept reveals that with proper transmission signalling design, different interference signals can in fact be aligned together, such that more radio resources can be assigned to the desired transmission. Although interference alignment can achieve a larger data rate compared to orthogonal transmission strategies, several challenges should be addressed to enable the deployment of this technique in future wireless networks For instance, to perform interference alignment, normally, global channel state information (CSI) is required to be perfectly known at all terminals. Clearly, acquiring such channel knowledge is a challenging problem in practice and proper channel training and channel state feedback techniques need to be deployed. In addition, since the channels are time-varying proper adaptive transmission is needed. This chapter review recent advances in practical aspects of interference alignment. It also presents recent test-bed implementations of signal processing algorithms for the realization of interference alignment.

  • 23.
    Nasiri Khormuji, Majid
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Coding Schemes for Relay Networks2011Doctoral thesis, monograph (Other academic)
    Abstract [en]

    Cooperative communications by pooling available resources—for example, power and bandwidth—across the network, is a distributed solution for providing robust wireless transmission. Motivated by contemporary applications in multi-hop transmission and ad hoc networks, the classical three-node relay channel (RC) consisting of a source–destination pair and a relay node has received a renewed attention. One of the crucial aspects of the communication over relay networks (RNs) is the design of proper relaying protocols; that is, how the relay should take part in the transmission to meet a certain quality of service.

    In this dissertation, we address the design of reliable transmission strategies and quantification of the associated transmission rates over RNs. We consider three canonical examples of RNs: the classical RC, the multiple-access RC (MARC) and the two-way RC.We also investigate the three-node RC and MARC with state. The capacity of the aforementioned RNs is an open problem in general except for some special cases. In the thesis, we derive various capacity bounds, through which we also identify the capacity of some new classes of RNs. In particular, we introduce the class of state-decoupled RNs and prove that the noisy network coding is capacity achieving under certain conditions.

    In the thesis, we also study the effect of the memory length on the capacity of RNs. The investigated relaying protocols in the thesis can be categorized into two groups: protocols with a finite relay memory and those with infinite relay memory requirement. In particular, we consider the design of instantaneous relaying (also referred to as memoryless relaying) in which the output of the relay depends solely on the presently received signal at the relay. For optimizing the relay function, we present several algorithms constructed based on grid search and variational methods. Among other things, we surprisingly identify some classes of semi-deterministic RNs for which a properly constructed instantaneous relaying strategy achieves the capacity. We also show that the capacity of RNs can be increased by allowing the output of the relay to depend on the past received signals as well the current received signal at the relay. As an example, we propose a hybrid digital–analog scheme that outperforms the cutset upper bound for strictly causal relaying.

  • 24.
    Nasiri Khormuji, Majid
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Relaying Protocols for Wireless Networks2008Licentiate thesis, comprehensive summary (Other scientific)
    Abstract [en]

    Motivated by current applications in multihop transmission and ad hoc networks, the classical three-node relay channel consisting of a source-destination pair and a relay has received significant attention. One of the crucial aspects of the relay channel is the design of proper relaying protocols, i.e., how the relay should take part into transmission. The thesis addresses this problem and provides a partial answer to that.

    In this thesis, we propose and study two novel relaying protocols. The first one is based on constellation rearrangement (CR) and is suitable for higher-order modulation schemes. With CR, the relay uses a bit-symbol mapping that is different from the one used by the source. We find the optimal bit-symbol mappings for both the source and the relay and the associated optimal detectors, and show that the improvement over conventional relaying with Gray mapping at the source and the relay can amount to a power gain of several dB. This performance improvement comes at no additional power or bandwidth expense, and at virtually no increase in complexity. The second one is a half-duplex decode-and-forward (DF) relaying scheme based on partial repetition (PR) coding at the relay. With PR, if the relay decodes the received message successfully, it re-encodes the message using the same channel code as the one used at the source, but retransmits only a fraction of the codeword. We analyze the proposed scheme and optimize the cooperation level (i.e., the fraction of the message that the relay should transmit). We compare our scheme with conventional repetition in which the relay retransmits the entire decoded message, and with parallel coding, and additionally with dynamic DF. The finite SNR analysis reveals that the proposed partial repetition can provide a gain of several dB over conventional repetition. Surprisingly, the proposed scheme is able to achieve the same performance as that of parallel coding for some relay network configurations, but at a much lower complexity.

    Additionally, the thesis treats the problem of resource allocation for collaborative transmit diversity using DF protocols with different type of CSI feedback at the source. One interesting observation that emerges is that the joint powerbandwidth allocation only provides marginal gain over the relaying protocols with optimal bandwidth allocation.

  • 25.
    Nasiri Khormuji, Majid
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Larsson, Erik G.
    KTH, School of Electrical Engineering (EES), Communication Theory.
    A spectrally efficient transmission scheme for half-duplex decode-and-forward relaying2007In: GLOBECOM 2007: 2007 IEEE GLOBAL TELECOMMUNICATIONS CONFERENCE, 2007, p. 1663-1667Conference paper (Refereed)
    Abstract [en]

    We propose a spectrally efficient transmission scheme for the half-duplex relay channel. In the proposed scheme, the relay combines N detected r-dimensional symbols and generates M new r-dimensional symbols, where M < N, using a linear transformation. The proposed linear transformation preserves the signal energy, and it facilitates decoupled symbol detection at the receiver.

    We also present an optimized design for the case of complex scalar modulation (r = 2) with N = 2 and M = 1. This design increases the spectral efficiency by 33% compared to conventional decode- or amplify-and-forward relaying.

  • 26.
    Nasiri Khormuji, Majid
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Larsson, Erik G.
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Analytical results on block length optimization for decode-and-forward relaying with CSI feedback2007In: 2007 IEEE 8th Workshop on Signal Processing Advances in Wireless Communications, IEEE , 2007, p. 96-100Conference paper (Refereed)
    Abstract [en]

    We consider block length optimization for collaborative transmit diversity using a decode-and-forward protocol assuming that the source and the relay have access to the magnitudes of all path gains. Moreover, we propose a simple scheme which requires only one bit of channel state information (CSI) feedback. We analyze the outage probabilities of all schemes for both selection combining and maximum ratio combining (MRC) at the destination. Analytical results show that even one bit of CSI feedback can provide a significant gain over conventional (non-adaptive) collaborative schemes.

  • 27.
    Nasiri Khormuji, Majid
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Larsson, Erik G.
    Department of Electrical Engineering (ISY), Linköping University.
    Cooperative Transmission Based on Decode-and-Forward Relaying with Partial Repetition Coding2009In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 8, no 4, p. 1716-1725Article in journal (Refereed)
    Abstract [en]

    We propose a novel half-duplex decode-and-forward relaying scheme based on partial repetition coding at the relay. In the proposed scheme, if the relay decodes the received message successfully, it re-encodes the message using the same channel code as the one used at the source, but retransmits only a fraction of the codeword. We analyze the proposed scheme and optimize the cooperation level (i.e., the fraction of the message that the relay should transmit). We compare our scheme with conventional repetition in which the relay retransmits the entire decoded message, with parallel coding, and additionally with dynamic decode-and-forward (DDF). We provide a finite-SNR analysis for all the collaborative schemes. The analysis reveals that the proposed partial repetition method can provide a gain of several dB over conventional repetition. It also shows that in general, power allocation is less important provided that one optimally allocates bandwidth. Surprisingly, the proposed scheme is able to achieve the same performance as that of parallel coding for some relay network configurations, but at a much lower complexity.

  • 28.
    Nasiri Khormuji, Majid
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Larsson, Erik G.
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Improving Collaborative Transmit Diversity by Using Constellation Rearrangement2007In: IEEE Wireless Communications and Networking Conference, WCNC, 2007, p. 804-808Conference paper (Refereed)
    Abstract [en]

    We propose an enhancement to cooperative transmit diversity based on uncoded detect-and-forward, by using so-called constellation rearrangement (CR) at the relay. With CR, the relay uses a bit-symbol mapping that is different from the one used by the source. We find the optimal bit-symbol mappings for both the source and the relay and the associated optimal detectors, and show that the improvement over conventional relaying with Gray mapping at the source and the relay can amount to a power gain of several dB. This performance improvement comes at no additional power or bandwidth expense, and at virtually no increase in complexity.

  • 29.
    Nasiri Khormuji, Majid
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Larsson, Erik G.
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Receiver Design for Wireless Relay Channels with Regenerative Relays2007In: IEEE International Conference on Communications, 2007, p. 4034-4039Conference paper (Refereed)
    Abstract [en]

    We develop a general framework for design of receivers for the wireless relay channel. We derive the optimum detectors for various degrees of channel state information (CSI) at the destination. We consider both the case when the destination has access to full knowledge of the CSI and the case when it only knows the statistics of the channel. High-SNR and low-SNR approximations of the detectors are presented as well.

  • 30.
    Nasiri Khormuji, Majid
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Capacity bounds and mapping design for binary symmetric relay channels2012In: Entropy, ISSN 1099-4300, E-ISSN 1099-4300, Vol. 14, no 12, p. 2589-2610Article in journal (Refereed)
    Abstract [en]

    Capacity bounds for a three-node binary symmetric relay channel with orthogonal components at the destination are studied. The cut-set upper bound and the rates achievable using decode-and-forward (DF), partial DF and compress-and-forward (CF) relaying are first evaluated. Then relaying strategies with finite memory-length are considered. An efficient algorithm for optimizing the relay functions is presented.The Boolean Fourier transform is then employed to unveil the structure of the optimized mappings. Interestingly, the optimized relay functions exhibit a simple structure. Numerical results illustrate that the rates achieved using the optimized low-dimensional functions are either comparable to those achieved by CF orsuperior to those achieved by DF relaying.In particular, the optimized low-dimensional relaying scheme can improve on DF relaying when the quality of the source-relay link is worse than or comparable to that of other links.

  • 31.
    Nasiri Khormuji, Majid
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Feedback capacity of the bidirectional broadcast channel2012In: 2012 Swedish Communication Technologies Workshop, Swe-CTW 2012, IEEE , 2012, p. 46-47Conference paper (Refereed)
    Abstract [en]

    This paper shows that feedback does not increase the capacity of the two-receiver discrete memoryless bidirectional broadcast channel.

  • 32.
    Nasiri Khormuji, Majid
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Input-distribution optimization for estimate-and-forward relaying2012In: Wireless Communication Systems (ISWCS), 2012 International Symposium on, IEEE , 2012, p. 201-205Conference paper (Refereed)
    Abstract [en]

    We investigate the design of optimized input distributions for the two-hop Gaussian relay channel under an average power constraint. In our study, the relay is confined to implement an estimate-and-forward strategy. We demonstrate that the rate achievable by an optimized discrete input distribution can significantly outperform that achievable by a Gaussian codebook. The lower bound obtained by the optimized EF scheme is also used to establish an improved lower bound on the rates achievable by compress-and-forward.

  • 33.
    Nasiri Khormuji, Majid
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    On the capacity of the binary symmetric relay channel with a finite memory relay2010In: IEEE Information Theory Workshop 2010, Cairo, 2010, Vol. ITW 2010Conference paper (Refereed)
    Abstract [en]

    We investigate capacity bounds for two instances of the binary symmetric relay channels. For one of these, we establish the capacity, and for the other one we present various capacity bounds. We first evaluate the cut-set bound and the rates achievable using decode-and-forward (DF) and compressand-forward (CF) relaying. We then focus on relaying strategies with finite memory-length and present an efficient algorithm for optimizing the relay functions. We use the boolean Fourier transform to unveil the structure of the optimized mappings. Interestingly, the optimized relay functions exhibit a simple structure. The numerical results show that the rates achieved using the optimized low-dimensional functions are either comparable or superior to those achieved by DF and CF relaying. In particular, the optimized low-dimensional relaying scheme can improve on DF relaying when the quality of the source-relay link is worse than or comparable to the quality of other links.

  • 34.
    Nasiri Khormuji, Majid
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Piecewise linear relaying: A low complexity parametric relaying2009In: SPAWC: 2009 IEEE 10TH WORKSHOP ON SIGNAL PROCESSING ADVANCES IN WIRELESS COMMUNICATIONS, NEW YORK: IEEE , 2009, p. 255-259Conference paper (Refereed)
    Abstract [en]

    We investigate the Gaussian, three-nodes relay channel with orthogonal receive components, i.e., the transmitted signals from the source and the relay do not interfere with each other. We develop and analyze low-complexity symbol-wise (as opposed to block-wise) relaying strategies based on a one-dimensional, parametric piecewise linear (PL) mapping. We numerically compute and optimize the achievable rates obtained by the PL mapping for a certain number of design parameters. We conclude that optimized PL relaying always outperforms conventional instantaneous linear relaying (amplify-and-forward). We also illustrate that the proposed PL relaying can improve on sophisticated block Markov encoding (i.e., decode-and-forward) when the source-relay link is ill-conditioned (relative to other links). Furthermore, PL relaying can work at rates close to those achieved by side-information encoding (i.e., compress-and-forward), but at a much lower complexity.

  • 35.
    Nasiri Khormuji, Majid
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Zaidi, Ali A.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Interference Management Using Nonlinear Relaying2010In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 58, no 7, p. 1924-1930Article in journal (Refereed)
    Abstract [en]

    We consider the three-node Gaussian relay channel where the relay observes a noisy version of the interference present in the source-destination link. We investigate three fundamental relaying approaches: linear relaying, memoryless nonlinear relaying, and compress-and-forward (CF). For interference-limited cases, we illustrate that optimized memoryless nonlinear relaying almost achieves the capacity.

  • 36.
    Yao, Sha
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Khormuji, Majid Nasiri
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Sawtooth relaying2008In: IEEE Communications Letters, ISSN 1089-7798, E-ISSN 1558-2558, Vol. 12, no 9, p. 612-614Article in journal (Refereed)
    Abstract [en]

    We consider the three-node AWGN relay channel with a memoryless relay, in contrast to the conventional decode-and-forward or compress-and-forward schemes, which require complex encoding and decoding processing at the relay. We model the operation of the relay as a single-variable deterministic mapping. We then in particular propose to use a "modulo function" or a "triangular function" to implement the mapping at the relay. Since both these have a sawtooth-like shape we coin the term "sawtooth relaying." We demonstrate significantly improved achievable rates of our proposed schemes over the conventional memoryless amplify-and-forward relaying.

  • 37.
    Zaidi, Ali A.
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Khormuji, Majid Nasiri
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Nonlinear transmission strategies for a general half-duplex AWGN relay channel2011In: 2011 IEEE Swedish Communication Technologies Workshop, Swe-CTW 2011, 2011, p. 58-61Conference paper (Refereed)
    Abstract [en]

    We consider the general AWGN relay channel consisting of a source node, a half-duplex relay node and a destination node. We propose a low-complex and memoryless nonlinear transmission scheme for delay sensitive applications. The proposed nonlinear strategy provides higher achievable transmission rates than those achieved by the existing linear strategy.

  • 38.
    Zaidi, Ali Abbas
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Nasir Khormuji, Majid
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Yao, Sha
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Optimized mappings for dimension-expansion relaying2009In: SPAWC: 2009 IEEE 10TH WORKSHOP ON SIGNAL PROCESSING ADVANCES IN WIRELESS COMMUNICATIONS, NEW YORK: IEEE , 2009, p. 474-478Conference paper (Refereed)
    Abstract [en]

    We study the three-node Gaussian relay channel consisting of a source, a relay and a destination. We assume that the relay is memoryless, i.e., the transmitted signal from the relay depends only on the currently received signal. Additionally, we focus on dimension expansion relaying, where the relay has access to more channel uses for retransmission. We use the end-to-end mutual information to numerically optimize the relay mappings. We present several examples for two types of source input alphabets: continuous (Gaussian and uniform) and discrete (uniform PAM). The maximum rate attained by using the optimized mappings is considerably improved compared to conventional linear relaying.

  • 39.
    Zaidi, Ali Abbas
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Nasir Khormuji, Majid
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Yao, Sha
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Rate-Maximizing Mappings for Memoryless Relaying2009In: 2009 IEEE INTERNATIONAL SYMPOSIUM ON INFORMATION THEORY, NEW YORK: IEEE , 2009, p. 694-698Conference paper (Refereed)
    Abstract [en]

    We study the problem of optimal design of relay mappings for the Gaussian relay channel in order to maximize the reliable transmission rate. We consider both Gaussian and modulation constrained signaling at the source. To optimize the relay mapping, we use an iterative integral equation as a necessary condition for optimality. The optimized relay mappings demonstrate significant rate improvement over conventional linear relaying (amplify-and-forward). The optimized mappings allow an efficient utilization of the side information received via the source destination link at the destination. Hence, the proposed mappings can be considered as an analog, memoryless approach to implementing compress-and-forward relaying with Wyner-Ziv compression in the relay.

  • 40.
    Zaidi, Ali Abbas
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Nasiri Khormuji, Majid
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Yao, Sha
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Optimized analog network coding strategies for the white Gaussian multiple-access relay channel2009In: 2009 IEEE Information Theory Workshop, 2009, Vol. ITW 2009, p. 460-464Conference paper (Refereed)
    Abstract [en]

    We consider a Gaussian multiple-access relay channel with multiple sources, a relay and a destination. We assume that the received signals at the relay and the destination from different nodes are orthogonal. Additionally, we assume that the relay performs an instantaneous mapping to compress all received signals from different sources into one output symbol. We refer to this as analog network coding. We optimize the analog network coding mapping to maximize the achievable sum rate. We additionally introduce an algorithm to obtain an achievable rate region. The optimized mappings are in general non-linear and provide superior rates compared to those of linear mappings.

1 - 40 of 40
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