This paper proposes a channel allocation principle that prevents TCP throughput degradation in multihop transmissions in a mesh network based on the carrier sense multiple access with collision avoidance (CSMA/CA) MAC protocol. We first address the relationship between the network topology of wireless nodes and the TCP throughput degradation based on computer simulations. The channel allocation principle is discussed in terms of resolution into a coloring problem based on throughput degradation. The number of required channels for the proposed channel allocation principle is evaluated and it is shown that two channels are sufficient for more than 96% simulated multihop patterns. The proposed channel allocation principle is extendable to generic mesh networks. We also clarify the number of required channels for mesh networks. The simulation results show that three channels are sufficient for more than 98% patterns in the generic mesh networks when the number of nodes is less than 10.

A multihop connection scheme, where one or more mobile terminals relay transmission signals using the same access scheme between an end user terminal and its destination base station, is a promising approach to overcome reduction in cell size caused by high bit-rate data transmission. In a general radio communication system, the coverage area and system throughput are closely interrelated. In this paper, the performance of a multihop cellular network employing a CDMA access scheme, which is a promising candidate for beyond the third generation, is studied in terms of the coverage area and system throughput by conducting a link level simulation. The results show that a multihop connection expands the coverage area, especially in the case of light traffic, and also has an advantage in system throughput.

Co-channel interference is a major factor limiting spectral efficiency of a cellular radio system. The trellis-coded co-channel interference canceller (TCC) leading to the significant increase of traffic capacity of a cellular system has been proposed. In this scheme, a maximum-likelihood sequence estimation implemented with the Viterbi algorithm is extended to estimate both desired signal and co-channel interference, and combined with trellis-coded modulation to enhance the co-channel interference cancelling capability. The complexity of TCC grows exponentially with the channel memory and the constraint length of the trellis encoder. In this paper, two reduced-state sequence estimation algorithms, namely, the delayed decision feedback sequence estimation and the M-algorithm, are applied to TCC and their performance is compared. In addition, effective trellis coded modulation schemes to reduce the computational complexity are proposed. The performance of these schemes is examined through simulations, and compared to that of a conventional interference canceller.

The binary parallel concatenated codes called turbo codes provide relatively large coding gains with reasonable computation complexity. The application of turbo codes to a coherent DS-CDMA mobile radio link with antenna diversity and coherent RAKE combining is considered. A soft-in/soft-out Viterbi decoder that requires less computation complexity is employed instead of maximum a posteriori probability (MAP) decoder. The effect of turbo codes on the achievable bit error rate (BER) performance in frequency selective multipath fading channels is evaluated by computer simulation. It is demonstrated that turbo codes can achieve better BER performance than convolutional codes having the same code rate for the relatively large interleaver size. How the coding gains are impacted by the interleaver size and constraint length of the turbo codes and by the propagation channel condition (power delay profile, the number of resolvable propagation paths, and the maximum Doppler frequency) is discussed.