Mobile communications with STBC and turbo codes

• Main Author: Torres, Paulo
• Publication Date: 2011
• Other Authors: Costa, Ludovic Mamede, Gusmão, António
• Format: Article
• Language: eng
• Source: Repositórios Científicos de Acesso Aberto de Portugal (RCAAP)
• Download full: http://hdl.handle.net/10400.11/7715
• topic: Alamouti; log-MAP; MAP; STBC

Users are increasingly demanding about the quality and consumer batteries of their mobile terminals to gain access to services imposed by operators. In order to satisfy the customers, operators must provide a good quality, high transmission rates to allow videoconferencing communications and low power consumption in mobile terminals, so that battery last longer. In mobile communications, data are transmitted over a channel that is affected by noise, thus affecting the quality of data received, and thus can degrade the received information. In traditional communications, SISO (Single-Input Single-Output systems) with one transmitting and one receiving antenna, are not efficient to minimize noise caused by the channel. Solutions such as increased bandwidth and increased power transmission would solve the problem, however, are not reliable. Although these solutions are valid in theory, none of them is put into practice, because increasing the transmission of mobile terminals, there would cause an increase in battery size, price and increasing the size of mobile terminals and the fact that it could be detrimental to our health. Increasing the bandwidth would be an easy way out and solve the problems of errors and low transmission rates, however there is a price to pay, the spectrum allocation is expensive, so this technique is not feasible. This paper aims to provide efficient solutions to improve the efficiency of power, namely to achieve a good quality with a low power consumption on the handset. The spectral efficiency is improved through the implementation of MIMO (Multi-Input Multi-Output) systems, i.e., multiple transmit antennas and multiple receiving antennas, using error correction codes. Through the union of these two techniques is possible to obtain a low error probability with low power consumption. This paper presents how MIMO solution the STBC (Space Time Block Codes) encoding. The Alamouti code [1] is used in this coding, which consists of data transmission with two transmit antennas and one or more receiving antennas. Other STBC codes for multiple antennas and multiple receiving antennas are presented in the paper, these codes developed by Tarokh et al [2]. The novelty of this study, presented here, is the use of MIMO systems using error correction codes (Turbo-codes[3]). In the turbo code decoding algorithms are used with soft outputs, as the MAP (Maximum a Posteriori) algorithm, Log-MAP and max-log-MAP. The error probability performance results, presented in this paper were obtained by Matlab Simulations with 4-QAM modulation in Rayleigh channel. The SISO systems are compared with MIMO systems with and without error correction. The simulation results show that there is a significant improvement when the MIMO systems are used compared to the SISO systems, and that with error correction lower error probability is achieved with lower energy consumption.