Yousef R. Shayan

Implementation of OFDM modem for the physical layer of IEEE 802.11a standard based on Xilinx Virtex-II FPGA

A prototype design, which is based on the orthogonal frequency division multiplexing (OFDM) technique, is presented for the physical layer of the IEEE 802.11a standard. Implementation aspects of an OFDM modem on a Xilinx field programmable gate array (FPGA) are addressed. The system includes synchronization circuitry used for packet detection and time synchronization. The demonstrated design flow shows an approach to implementing and prototyping the architecture of a real-time base-band OFDM modem. This design is efficiently synthesized on a 0.15 /spl mu/m/0.12 /spl mu/m CMOS 8-layer metal process Virtex-II FPGA. The resulting hardware implementation is analyzed and simulated for a system clock speed of 72 MHz to verify adequate performance.

A versatile time-domain Reed-Solomon decoder

A versatile Reed-Solomon (RS) decoder structure based on the time-domain decoding algorithm (transform decoding without transforms) is developed. The algorithm is restructured, and a method is given to decode any RS code generated by any generator polynomial. The main advantage of the decoder structure is its versatility, that is, it can be programmed to decode any Reed-Solomon code defined in Galois field (GF) 2/sup m/ with a fixed symbol size m. This decoder can correct errors and erasures for any RS code, including shortened and singly extended codes. It is shown that the decoder has a very simple structure and can be used to design high-speed single-chip VLSI decoders. As an example, a gate-array-based programmable RS decoder is implemented on a single chip. This decoder chip can decode any RS code defined in GF (2/sup 5/) with any code word length and any number of information symbols. The decoder chip is fabricated using low-power 1.5- mu , two-layer-metal, HCMOS technology. >

Performance evaluation of multihop ad hoc WLANs

Ongoing technological advances in portable devices, coupled with the need for continuous connectivity while mobile, have made ad hoc networks a compelling research and development topic, particularly in a challenging multimedia multihop scenario. The ability of IEEE 802.11s ad hoc mode of operation, as a dominating wireless local area network (WLAN) protocol, to serve multihop networks requires thorough investigation. In this article, through considering crucial real-life physical phenomena and avoiding as many confining assumptions as possible, system performance measures such as delay and packet failure rate are evaluated. As a result, the importance of adequate selection of the system parameters toward performance improvement is underscored. Moreover, the simulation results imply that by complementing through priority provisions, coordination, route reservation, clustering, and optimum channel coding considerations, the IEEE 802.11 medium access control (MAC) protocol can survive in a multihop scenario. The custom simulation environment developed features modularity, comprising traffic generator, mobility, wireless channel, and IEEE 802.11 protocol modules, and is capable of accommodating many more of the physical phenomena involved.

On the code and interleaver design of broadband OFDM systems

In this letter, we study the performance of space-frequency-coded orthogonal frequency-division modulation systems over multiple-input multiple-output frequency-selective channels. The diversity and coding advantages are derived in terms of the minimum Hamming distance and the minimum squared product distance of the code as well as the relative frequency locations (tones) where a pair of codewords with the minimum Hamming distance differ. These relationships between performance and well-defined code parameters provide new insight to code construction and interleaving design. In addition, we propose a block interleaver that yields nearly optimal coding advantage for space-frequency trellis codes.

A cellular structure for a versatile Reed-Solomon decoder

A new cellular structure for a versatile Reed-Solomon (RS) decoder is introduced based on time domain decoding algorithm. The time domain decoding algorithm is restructured to be suitable for introducing the cellular structure. The main advantages of this structure are its versatility and very simple cellular structure. By versatile decoder we mean a decoder that can be programmed to decode any (n, k) RS code defined in Galois field 2/sup m/ with a fixed block length n and a fixed symbol size m. This decoder can correct both errors and erasures for any message length k. The introduced decoder is cellular and has a very simple structure and hence it is suitable for VLSI designs.

Design of Reed-Solomon (16,12) codec for North American Advanced Train Control System

The design of the codec for the ATCS radio data link is considered. The code is defined. The encoding algorithm, the decoding algorithm, and Galois field arithmetic are discussed. Implementation of the Reed-Solomon codec as a stand-alone system in order to provide a possibility of real-time bit-rate measurement is discussed. The implementation of this codec using three different 8-b and 16-b microprocessors/microcomputers is described. Their complexity and throughput are discussed. >

Modified time-domain algorithm for decoding Reed-Solomon codes

A technique for reducing the number of inversions in the time-domain decoding algorithm based on an algebraic decoder (Blahuts decoder) is introduced. It is proved that the modified algorithm is equivalent to the original one. The modified algorithm can be used in the universal Reed-Solomon decoder to decrease complexity. >

Cross-layer optimization for wireless mesh networks with smart antennas

A cross-layer optimization framework for wireless mesh networks is presented where at each node, various smart antenna techniques such as beam-forming, spatial division multiple access and spatial division multiplexing are employed. These techniques provide interference suppression, capability for simultaneous communication with several nodes and transmission with higher data rates, respectively, through multiple antennas. By integrating different combinations of the multi-antenna techniques in physical layer with various constraints from MAC and network layers, three Mixed Integer Linear Programming (MILP) models are presented to minimize the system activation time. Since these optimization problems are complex combinatorial, the optimal solution is approached by a Column Generation decomposition method. The numerical results for different network scenarios with various node densities, number of antennas, transmission ranges and number of sessions are provided. It is shown that the resulted directive, multiple access and multiplexing gains combined with scheduling, effectively increase both the spectrum spatial reuse and the capacity of the links and therefore, enhance the achievable system throughput. Our cross-layer approach is also extended to consider heterogeneous networks and we present a multi-criteria optimization framework to model the design problem where the objective is to jointly minimize the cost of deployment and the system activation time. Our results reveal the benefits of joint design in terms of reducing the cost of deployment while achieving higher system performance.

On the diversity order of space-time trellis codes with receive antenna selection over fast fading channels

In this paper, we study the performance of space-time trellis codes (STTCs) with receive antenna selection over fast fading channels. Specifically, we derive upper bounds on the pairwise-error probability (PEP) with antenna selection. In performing the selection, we adopt a criterion that is based on using L out of the available M receive antennas that result in maximizing the instantaneous signal-to-noise ratio (SNR) at the receiver, where L les M. We show that the diversity order resulting from antenna selection deteriorates significantly and is actually dictated by the number of selected antennas. The implication of this result is that adding more receive antennas, while maintaining the same number of selected ones, will have no impact on the diversity order, but it does, however, provide some additional coding gain. This is unlike the case for quasi-static fading channels in which the diversity order is always preserved with antenna selection when the underlying STTC is full-rank. We present numerical examples that support our analysis

Outage probability in a circle with uniformly distributed users

Outage probability is one of the most important metrics that can be used to study the performance of wireless networks. In this paper, we evaluate outage probability of users which are uniformly distributed in a circular cell. The outage probability is determined in terms of generic parameters and is compared with well-known formula of the percentage of cell coverage area. Simulation is performed in order to confirm the analytical results.