Optimizing time and space MIMO antenna system for frequency selective fading channels

Smart or adaptive antennas promise to provide significant increases in system capacity and performance in wireless communication systems. In this paper, we investigate the use of adaptive antennas at the base and mobile stations, operating jointly, to maximize the average signal-to-interference and noise ratio (SINR) of each packet in the system for frequency selective channels with prior knowledge of the channel at the transmitter. Our approach is based on deriving an analytic formula for the average packet SINR and using the Lagrange multiplier method to determine an optimum. We derive necessary conditions for an optimum solution and propose an analytical expression for the optimum. Our analytical expression is not guaranteed to be the global optimum but it does satisfy the derived necessary conditions and, in addition for frequency flat channels, our results reduce to expressions for optimal weights previously published. To demonstrate the potential of the proposed system, we provide Monte Carlo simulation results of the system bit-error rates and make comparisons with other adaptive antenna systems. These show that significant improvements in performance are possible in a wireless communications context

Performance enhancement of multiuser MIMO wireless communication systems

This paper describes a new approach to the problem of enhancing the performance of a multiuser multiple-input-multiple-output (MIMO) system for communication from one base station to many mobile stations in both frequency-flat and frequency-selective fading channels. This problem arises in space-division multiplexing systems with multiple users where many independent signal streams can be transmitted in the same frequency and time slot through the exploitation of multiple antennas at both the base and mobile stations, Our new approach is based on maximizing a lower bound for the product of signal-to-interference plus noise ratio (SINR) of a multiuser MIMO system. This provides a closed-form (noniterative) solution for the antenna weights for all the users, under the constraint of fixed transmit power. Our solution is shown by simulation to have better performance than previously proposed iterative or noniterative solutions. In addition, our solution requires significantly reduced complexity over a gradient search-based method that directly optimizes the product SINgs while still maintaining similar performance. Our solution assumes channel state information is present at the base station or transmitter

2nd IEEE International Mediterranean Conference on Communications and Networking (IEEE MeditCom 2022) 5-8 September 2022, Athens, Greece

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THE PERFORMANCE OF OPTICAL-FIBER DIRECT-SEQUENCE SPREAD-SPECTRUM MULTIPLE-ACCESS COMMUNICATIONS-SYSTEMS

Because of the random nature of the photodetection process and the multiple-user interference, an exact analysis of avalanche photodiode (APD)-based optical code division multiple-access (CDMA) communications systems is intractable and quite often, Monte Carlo (MC) simulations which yield exact estimates of system performance in terms of bit error rates (BER's) require a prohibitive computational burden. In this paper, a quick and accurate MC method for simulating APD-based optical CDMA systems is presented. In particular, a performance analysis of optical CDMA systems employing optical orthogonal and prime Sequence codes is undertaken

Adaptive resource allocation for multiaccess MIMO/OFDM systems with matched filtering

In this letter, we propose an adaptive resource-allocation algorithm for multiaccess multiple-input multiple-output/orthogonal frequency-division multiplexing systems. The proposed algorithm endeavors to maximize the system power efficiency, given that the users' quality of service (QoS) requirements, specified by bit-error rate and data rate, are satisfied. Subcarrier allocation, power distribution, and modulation for multiple users are jointly optimized according to users' channel states and QoS requirements. To avoid the joint optimization of resource allocation and beamforming, matched-filter-based receivers are employed at the base station, with cochannel interference being mitigated through dynamic subchannel allocation. A neighborhood search scheme is further developed to obtain a good allocation solution with reasonable computational efforts. Our results show that the proposed algorithm is able to achieve significant enhancement in the system power efficiency due to the successful exploitation of multiuser diversity, as well as channel variations in the time, frequency, and space domains

The use of WMC distribution for performance evaluation of APD optical communication systems

In the analysis of the bit-error rate (BER) of an optical communication system with avalanche photodiode (APD) detectors, the Webb, McIntyre, Conradi (WMC) distribution has been often used to approximate the APD receiver output statistics, This paper presents new simple and closed form BER expressions as well as an importance sampling technique for optical systems employing APD receivers when the WMC model is used. Comparison of the WMC model with the exact model is also carried out, In particular, it is shown that the WMC distribution is quite accurate and has the advantage of simplicity for both simulation and analysis

Performance analysis of DS-UWB multiple access under imperfect power control

Ultra-wideband (UWB) technology is characterized by transmitting extremely short duration radio impulses. To improve its multiple-access (MA) capability, UWB technology can be combined with traditional spread-spectrum techniques. So far, much of the research has focused on perfect power-control conditions and on employing time-hopping spread-spectrum with impulse radio using pulse-position modulated signals. In this letter, we outline the attractive features of direct-sequence (DS) UWB MA systems employing antipodal signaling and compare it with time hopping. Performance of DS-UWB communication systems, in terms of MA capability and bit-error rate performance, are evaluated under both perfect and imperfect power-control conditions. An upper bound on the total combined bit-transmission rate is derived

Cross-layer design for combining cooperative diversity with truncated ARQ in ad-hoc wireless networks

We propose a cross-layer design which combines truncated ARQ at the link layer and cooperative diversity at the physical layer. In this scheme, both the source node and the relay nodes utilize an orthogonal space-time block code for packet retransmission. In contrast to the previous cooperative diversity protocols, here cooperative diversity is invoked only if the destination node receives an erroneous packet from the source node. In addition, the relay nodes are not fixed and are selected according to the channel conditions using CRC. It will be shown that this combination of adaptive cooperative diversity and truncated ARQ can greatly improve the system throughput compared to the conventional truncated ARQ scheme and fixed cooperative diversity protocols

Concatenated coding for DS/CDMA transmission in wireless communications

In this work, me investigate the use of forward-error correction (FEC) as well as concatenated coding for reliable data transmission in asynchronous direct-sequence code division multiple-access communications over frequency-selective Rayleigh fading channels. The FEC scheme combines antenna diversity with low complexity concatenated codes which consist of a Reed-Solomon outer code and a convolutional inner code. Under this concatenated coding scheme, we analyze the average bit-error rate performance and capacity tradeoffs between various system parameters under a fixed total bandwidth expansion and concatenated codes constraint requirements