Multiuser orthogonal frequency division multiplexing (OFDM) with adaptive multiuser subcarrier allocation and adaptive modulation is considered. Assuming knowledge of the instantaneous channel gains for all users, we propose a multiuser OFDM subcarrier, bit, and power allocation algorithm to minimize the total transmit power. This is done by assigning each user a set of subcarriers and by determining the number of bits and the transmit power level for each subcarrier. We obtain the performance of our proposed algorithm in a multiuser frequency selective fading environment for various time delay spread values and various numbers of users. The results show that our proposed algorithm outperforms multiuser OFDM systems with static time-division multiple access (TDMA) or frequency-division multiple access (FDMA) techniques which employ fixed and predetermined time-slot or subcarrier allocation schemes. We have also quantified the improvement in terms of the overall required transmit power, the bit-error rate (BER), or the area of coverage for a given outage probability.

In the first part, an iterative receiver for joint channel estimation and cochannel interference cancellation suitable for time-division multiple-access (TDMA) cellular radio systems is proposed. The receiver is based on joint maximum-likelihood sequence estimation (JMLSE). It is blind with respect to the data of the interfering users but training-based with respect to the data of the desired user and is therefore referred to as semi-blind. As opposed to concurrent receiver structures where the number of receiving antennas must exceed the number of cochannel interferers, the proposed receiver is suitable for just one receive antenna. No knowledge on the burst structure of the interferer is used. Hence, the proposed receiver is suitable for (but not restricted to) the downlink in asynchronous networks. The proposed receiver is able to operate at a signal/interference ratio of 0 dB in asynchronous GSM/GPRS networks given a single dominating interferer. Furthermore, the results indicate that with proper interference cancellation it is not necessary to synchronize GSM/GPRS networks.

Abstract — Coded transmission over channels introducing intersymbol interference in presence of a co-channel interferer and additive white Gaussian noise poses a problem for single antenna receivers. In this context we present a bidirectional listsequential (LISS) interference canceller which performs joint detection of the desired user and the interferer. The treebased LISS algorithm is derived from a decoding technique for convolutional codes with high memory, namely sequential decoding, and adapted to the soft-in/soft-out detection problem. Due to bidirectional tree-searching with two independent LISS algorithms, the proposed detector allows parallel processing with a controllable complexity even for high memory channels. I.

ALOHA systems are some of the most attractive options for wireless applications which include packet transmission. However, despite their flexibility and simplicity, they present a very lowchannel throughput. The objective of this paper is to analyze the performance of Slotted ALOHA based vertical layered space-time, known as V-BLAST, systems over wireless links. The multiple transmit antennas in VBLAST are treated as individual mobile station transmitters, while the base station consists of multiple receive antennas. The V-BLAST algorithm is then invoked to jointly detect the signals from all users at the same time. To demonstrate the potential of the proposed multiple-input multiple-output (MIMO) system, we first consider the performance of V-BLAST in a circuit-switched flat fading environment for a variety of system parameters. Then, the throughput and delay performance are analyzed under different packetized traffics.