IEEE Transactions on Wireless Communications

Low density generator matrix (LDGM) codes are a particular class of low density parity check (LDPC) codes with very low encoding complexity. Single LDGM codes present high error-floors, which can be substantially reduced with the serial concatenation of two LDGM (SCLDGM) codes. We propose a technique to obtain good SCLDGM codes using extrinsic information transfer (EXIT) functions in a novel way. ... View full abstract»

In this paper we develop a multiple input multiple output (MIMO) channel model and derive its spatial and temporal correlation properties. We present a generalized methodology to derive the spatial correlation when the angles of arrival (AoA) and angles of departure (AoD) are either independent or partly correlated. Our model therefore spans the full range from well-established single ring models,... View full abstract»

This work investigates the following question: subject to strictly limited (finite-rate) feedback in a multi-user multi-antenna system, what channel state information (CSI) should we send back to the transmitter, and how should it be used? Considering the class of single-beam systems, we suggest a combination of beamforming (array gain) and multi-user diversity. It has been shown that in single an... View full abstract»

The bit-error rate (BER) analysis for BPSK pre-detection maximal ratio combining (MRC) systems in two-wave with diffuse power (TWDP) fading is presented. In TWDP fading, the received signal is composed of two specular components in addition to the diffuse signal. The analysis shows that in TWDP fading, the BER of the MRC system is given by the weighted sum of the BERs of a number of MRC systems in... View full abstract»

In conventional CDMA receivers, the detection of multipath components and RAKE finger management is normally based on the received signal energy per path. These schemes essentially overlook the interference component contaminating the total received power. Consequently, they exhibit poor multipath detection capability especially at low signal-to-interference-plus-noise ratio (SINR). In this paper,... View full abstract»

In this paper, the inverse discrete Fourier transform (IDFT) results of oversampled Walsh Hadamard (WH) sequences and WH-based complementary (CP) sequences are derived, based on which, the peak factors (PF) of MC-CDMA signals are investigated for both the two sequence sets. The upper bounds of PF for both BPSK and QPSK modulation are presented in this paper and the PF bounds presented in B.J. Choi... View full abstract»

The performance of dual-branch predetection switch-and-stay combining (SSC) in correlated Rician fading is considered in conjunction with several modulation formats. Analytical expressions are derived for the average symbol error rate (SER) of predetection SSC in correlated Rician fading. Switching thresholds that minimize the average SER are obtained. The impact of fading factor and the fading co... View full abstract»

This work analyzes the throughput of Go-Back-N (GBN) in block fading, a model frequently used for slow fading wireless channels. We devise hidden Markov models and block transition probabilities for the block fading channel, allowing us to calculate the throughput of GBN with reliable feedback, as well as unreliable feedback. The advantages of this approach include generality: it applies to two-st... View full abstract»

We consider a two-hop MIMO-OFDM communication scheme with a source, an amplify-and-forward relay, and a destination. We examine the possibilities of power allocation (PA) over the subchannels in frequency and space domains to maximize the instantaneous rate of this link if channel state information at the transmitter (CSIT) is available. We consider two approaches: (i) separate optimization of the... View full abstract»

Recent work in literature suggests the use of companding transforms to reduce the peak to average power ratio (PAPR) of orthogonal frequency division multiplexing (OFDM) systems. However, previous performance evaluations assume the availability of infinite bandwidth. In bandlimited conditions, the performance deteriorates as a result of filtering out the out-of-band radiation (OBR). In this letter... View full abstract»

We propose a simple distributed radio resource allocation algorithm for an OFDMA cellular system, which aims at minimizing the overall transmitted power subject to a rate constraint for each user. In order to reduce the problem complexity we use a single modulation; simulations show that the resulting performance degradation is negligible when the number of users is high enough. Moreover, we propo... View full abstract»

Free space optical (FSO) communications is a cost-effective and high bandwidth access technique, which has been receiving growing attention with recent commercialization successes. A major impairment in FSO links is the turbulence- induced fading which severely degrades the link performance. To mitigate turbulence-induced fading and, therefore, to improve the error rate performance, spatial divers... View full abstract»

Energy-constrained multihop wireless links are considered, where the total power consumption is minimized under given requirements on the end-to-end bit error rate (BER). As multihop transmissions are known to be able to save transmission energy in a wireless environment, we study the optimal power scheduling schemes over intermediate hops when the source- relays-destination link can be modeled as... View full abstract»

In this paper, the performance of IEEE 802.15.4 ZigBee under the interference of IEEE 802.11b wireless local area network (WLAN) and/or Bluetooth is evaluated using an analytic model for the coexistence among ZigBee, WLAN, and Bluetooth. The packet error rate (PER) is evaluated, where the PER is obtained from the bit error rate (BER) and the collision time. The BER is obtained from the signal-to-i... View full abstract»

We study pulse-based ultra wideband (UWB) communications over multipath channels using asynchronous spread spectrum (SS) multiple access (MA) based on time-hopping (TH) and pulse position modulated (PPM) signals. More specifically, we analyze the signal-to-interference (SIR) degradation in the presence of additive white Gaussian noise (AWGN), multi-user interference (MUI), and dense multipath effe... View full abstract»

The problem of signal design for bandwidth-efficient multiple access (BEMA) over additive white Gaussian noise (AWGN) channels is addressed under quality of service (QoS) requirements specified by asymptotic effective energies (AEEs). The AEE characterizes the bit error rate (BER) in the low-noise regime, but in contrast to BER, it is tractable and amenable to analysis and signal design. We adopt ... View full abstract»

Theoretical capacity calculations and corresponding simulations show significant capacity/throughput gains from MIMO systems. Whether these gains are achievable in a real system, deployed in a practical environment, depends on a variety of factors, such as the choice of the communication algorithms, analog impairments and the "quality" of the wireless channel to sustain MEMO communications. In thi... View full abstract»

We investigate the ability of serially-concatenated low density generator matrix (SCLDGM) codes to approach the capacity of ergodic multiple-input multiple-output (MIMO) channels. First, we explain how to design good SCLDGM codes using extrinsic information transfer (EXIT) analysis and optimum detection. However, optimum detection becomes unfeasible in many cases of practical interest where the nu... View full abstract»

This paper proposes a cross-layer scheduling scheme for OFDMA wireless systems with heterogeneous delay requirements. We shall focus on the cross-layer design which takes into account both queueing theory and information theory in modeling the system dynamics. We propose a delay-sensitive cross-layer design, which determines the optimal subcarrier allocation and power allocation policies to maximi... View full abstract»

Time-varying multipath channels distort the orthogonality between subchannels in orthogonal frequency-division multiplexing (OFDM) transmission. The loss of sub-channel orthogonality causes inter-subchannel interference (ICI), which limits the achievable bit-error probability (BEP) at high signal-to-noise ratio (SNR). In this paper, we propose a simple but very effective ICI self-cancellation algo... View full abstract»

We consider the allocation of power across forward-link packets in a wireless data network. The packets arrive according to a random (Poisson) process, and have fixed length so that the data rate for a given packet is determined by the assigned power and the channel gain to the designated user. Each user's service preferences are specified by a utility function that depends on the received data ra... View full abstract»

Multiple-input-multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems have recently attracted substantial research interest. However, compared to single-input-single-output (SISO) systems, channel estimation in the MIMO scenario becomes more challenging, owing to the increased number of independent transmitter-receiver links to be estimated. In the context of the Bell lay... View full abstract»

For a fading Gaussian multiple access channel with user cooperation, we obtain the power allocation policies that maximize the average rates achievable by block Markov superposition coding, subject to average power constraints. The optimal policies result in a coding scheme that is simpler than the one for a general multiple access channel with generalized feedback. This simpler coding scheme also... View full abstract»

The emergence of wireless sensor networks has imposed many challenges on network design such as severe energy constraints, limited bandwidth and computing capabilities. This kind of networks necessitates network protocol architectures that are robust, energy-efficient, scalable, and easy for deployment. This paper proposes a robust energy-aware clustering architecture (REACA) for large-scale wirel... View full abstract»