In this paper, the authors focus on upstream transmission in TDMA-based IEEE 802.16j and propose two time slot assignment algorithms to decrease end-to-end transmission latency. One of the proposed algorithms assigns time slots considering the hop count from a gateway node, and the other takes the path from the relay node to the gateway node into account. In addition, a restriction in assigning time slots is introduced to reduce the delay at each relay node. The algorithms with the restriction assign later time slots considering the time slot order of links connecting a relay node. The performance of the proposed algorithms is evaluated through simulation experiments from the viewpoints of frame size and end-to-end transmission latency, and it is confirmed that the proposed algorithms achieve small transmission latency regardless of packet generation rate in the network, and decrease the transmission latency by up to 70% compared with the existing algorithm.

An Ad Hoc network is a collection of wireless mobile nodes dynamically forming a temporary network without the use of any existing network infrastructure or centralized administration. The choice of medium access is difficult in Ad Hoc networks due to the time-varying network topology and the lack of centralized control. In this paper, we propose a novel multichannel schedule-based Medium Access Control (MAC) protocol for Ad Hoc networks named Multichannel Reservation Protocol for TDMA-based networks (MRPT). MRPT ensures collision free in successfully reserved data links, even when hidden terminals exist. The reservation of MRPT is based a control channel and in order to improve throughput we propose Four-Phase-Two-Division (FPTD) as a media access scheme of the control channel for broadcasting control or reservation messages. In FPTD, the collision can be solved rapidly with an efficient backoff algorithm which results in that system block is avoided in case of high traffic. In this paper, we also present the throughput performance of MRPT, which shows a high value and no system block even in case of high traffic load.

This paper describes the results of a series of laboratory experiments for performance evaluations of our proposed Maximum Likelihood Sequence Estimation (MLSE) based interference canceller, the Interference Canceling Equalizer (ICE), which can cancel both co-channel interference (CCI) and inter-symbol interference (ISI). To verify the feasibility of ICE for the Japanese cellular communications system, a standard of which has been released under the name of Personal Digital Cellular (PDC) system, a prototype system was constructed using 27 TI TMS320C40 Digital Signal Processor (DSP) chips. The ICE prototype works in real-time on the PDC air interface, major specifications of which are π/4 QDPSK 21 k symbols/s 3-channel time-division multiple-access (TDMA). Two-branch diversity reception is used to enhance the signal detection performance of ICE. In the experiments, BER performances were evaluated using the prototype system. Under a single-path Rayleigh fading and a single CCI condition, the ICE receiver attains the BER of less than 310-2 with the negative values of the average CIR: for fD = 5 Hz and 40 Hz, the average CIR more than -20 dB and -10 dB, respectively. Under a double-path Rayleigh fading and a single CCI condition, the ICE receiver attains the BER of less than 1.510-2 with the negative values of the average CIR: for fD = 5 Hz and 40 Hz, the average CIR more than -20 dB and -10 dB, respectively. The laboratory test results suggest that the ICE receiver has potential for system capacity enhancement.