M.R. Soleymani

An Efficient Nearest Neighbor Search Method

A simple, but efficient, nearest neighbor search algorithm is proposed and simulation results demonstrating its effectiveness in the case of vector quantization for a given source are presented. The simulation results indicate that use of this approach reduces the number of multiplications and additions to as low as 9 percent of those required for the conventional full search method. The reduction in the number of subtractions is also considerable. The increase in the number of comparisons is moderate, and therefore, the total number of operations can be as low as 28 percent of those required by the full search method. An additional advantage of the described algorithm is the fact that it requires no precomputations and/or extra memory.

On the BER Performance of Space-Frequency Block Coded OFDM Systems in Fading MIMO Channels

Closed-form expressions for the bit error rate (BER) performance of space-frequency block coded OFDM (SFBC-OFDM) systems are derived and evaluated for frequency-selective fading channels. In the performance analysis, both M-ary phase shift keying (MPSK) and M-ary quadrature amplitude modulation (MQAM) are considered, and the effects of channel estimation errors on the BER performance are studied. Numerical results and comparisons are provided for several forms of SFBC-OFDM. It is shown that the results obtained from the closed-form formulae are very close to the ones using the exact expressions and to simulation results of the SFBC-OFDM model. The BER deterioration that results from channel estimation errors in the SFBC-OFDM systems is also illustrated. Using the provided results, the amount of degradation can be quantified.

A fast MMSE encoding technique for vector quantization

The authors present a very efficient minimum mean-squared error (MMSE) encoding method useful for vector quantization. Using this method results in a considerable reduction in the number of multiplications and additions. The increase in the number of comparisons is moderate, and therefore the overall saving in the number of operations is still considerable. Very little precomputation and extra storage is required. >

Combine LDPC Codes Over GF(q) With q-ary Modulations for Bandwidth Efficient Transmission

Low-density parity-check (LDPC) codes are playing more and more important role in digital broadcasting standards due to their excellent error correction performance. In this paper, we study the combination of LDPC codes over GF(q) with q-ary modulations for bandwidth efficient transmission over AWGN channel and consider the design of the codes. Specifically, we develop the concept of quasi-regular codes, and propose an improved Monte Carlo method to optimize the quasi-regular codes. To justify the performance of our proposed scheme, simulation results are presented and analysed.

The effect of the frequency offset on the probability of miss in a packet modem using CFAR detection method (satellite communication)

The effect of frequency offset on the probability of miss for a packet radio modem, using the constant false alarm rate (CFAR) preamble detection scheme, is analyzed. The expression for the probability of miss for the general case, i.e., where there is a frequency offset, is derived. This general expression is then used to derive the expressions for the false alarm rate and the probability of miss for the special case where the frequency offset is negligible. Several graphs depicting the probability of miss for different values of signal-to-noise ratio and frequency offset are also included. >

A high-speed search algorithm for vector quantization

In this work, we present a very efficient search method useful for vector quantization, and other nearest neighbor search problems. The algorithm first finds a small area around the input vector with one codevector on its boundary. After finding such an area, the codebook is searched to determine whether there is any other codeword inside this area or not. This search is performed employing two tests, avoiding distortion calculation for those codewords which fail these tests. Using this algorithm the saving in the number of multiplications can be over 99%, in comparison with the conventional full search method, with the number of additions being reduced by as much as 82%. The price paid is a moderate increase in the number of comparisons.

Design of lossless turbo source encoders

Lossless turbo source coding with decremental redundancy is an effective approach for compressing binary sources. A large block length lossless turbo source encoder offers compression rates close to the source entropy but with large latency. In this letter, we propose a lossless compression technique for binary memoryless sources using short block length turbo codes. To achieve compression rates close to the source entropy, we modify different components of the encoder. We focus on the design of the parity interleaver for different compression rates. Also, we replace the square shape puncturing array with a rectangular shape array that allows finer puncturing and hence improved compression rates. Finally, instead of a single code, we employ many codes operating in parallel. Given these modifications, we evaluate the encoding complexity of the proposed code

A subspace scheme for blind user identification in multiuser DS-CDMA

A subspace approach for user identification in a synchronous multiuser code division multiplex access (CDMA) is suggested. In this scheme, prior knowledge of the spreading codes and user powers is not required. The spreading codes and the corresponding received amplitudes are both estimated are both estimated from the received signal, and are used to identify the active users. Eigenvalue decomposition (EVD) is performed on the received signal and through a recursive algorithm, the spreading codes and the received powers are estimated. Simulation results indicate that the approach is capable of identifying the active users and their related powers without relying on any prior information.

Variable-rate OFDM systems with selective antenna diversity and adaptive modulation

In this article, a new scheme consisting of a combination of adaptive modulation, orthogonal frequency division multiplexing (OFDM), high order space-frequency block coding (SFBC), and antenna selection is presented. The proposed scheme, exploits the benefits of space-frequency block codes, OFDM and adaptive modulation to provide high quality of transmission for wireless communications over frequency selective fading channels. We examine the spectral efficiency and coding gain advantages of the proposed system. It is shown that antenna selection with adaptive modulation can greatly improve the performance of the conventional SFBC-OFDM systems.

The Effect of Antenna Physics on Fading Correlation and the Capacity of Multielement Antenna Systems

In this paper, we investigate the effects of antenna directivity and antenna orientation on fading correlation and, therefore, the channel capacity in multiple-input-multiple-output communication systems by means of a spherical simulation model. The correlation is caused by the mutual interaction of the scattering environment and antenna elements. To study the effect of antenna directivity and orientations on the correlation and channel capacity in a more realistic environment, we extend the ldquoone-ringrdquo model to a spherical scattering environment, which is appropriate for narrowband 3D Rayleigh fading. In our model, scatterers around a subscriber unit are distributed over a sphere centered on the antenna array in the subscriber unit. Antenna directivity is included in a precise way, and the antenna array can be placed in any orientation. Any type of antenna can be studied in the model. Through simulation, we find that directive antenna elements in linear broadside arrays make the channel capacity more strongly directive than when antenna elements are isotropic. Moreover, different antenna patterns and orientations have different outage capacities depending on the interaction of antenna directivities and the incident waves, which shows that the antenna pattern and orientation affect the channel capacity to some extent. In the uniformly scatter-rich environment, the microstrip antenna array can have 10% higher outage capacity than that of the dipole antenna array.