|Abstract: ||Abstract: There has been an interesting issue in multimedia communications over wireless system in recent years. In order to achieve high data rate wireless multimedia communications, spatial multiplexing technique (Foschini & Gans, 1998; Wolniansky et al. 1998) has recently developed as one of the most noteworthy techniques as multiple-input and multiple-output (MIMO) systems. If the channel state information is perfectly available at the transmitter (Driessen & Foschini, 1999; Burr, 2003), we can maximize the channel capacity to design a realizable video transmission system. Under channel capacity limitation, the chapter presents how to employ joint source-channel coding algorithm with adequate modulation techniques to get the possibly best performance in the system design. Adaptive video coding to the varying channel conditions in real-time is well matched to MIMO systems for an optimized video transmission. An important matter in designing adaptive video transmission system is how often the feedback of the channel state information should be carried out. In fact, the feedback interval is mainly decided by the channel characteristics. For wireless fading channels, the feedback information needed to be able to capture the time varying channel characteristics for a true adaptive transmission. Song & Chen (2007, 2008) proposed adaptive algorithm design to utilized partial channel state information from receiver for layered scalable video coding (SVC) transmission over MIMO system. There are some interesting topics related in adaptive video transmission over wireless multimedia communication systems can be found in (Chen & He, 2006). In our proposed system, we investigate the system performance of a joint MPEG-2 coding scheme with convolutional channel coding and space time block coding (STBC) techniques, associated with suitable modulation method (BPSK or QPSK), for video data transmission over a wireless MIMO system with Rayleigh fading noises. Rates assigned to MPEG-2 source code and convolutional channel code as well as space-time block code schemes are based on the feedback information from Performance Control Unit (PCU) under system channel capacity limitation, which ensures the proposed system achieved the best performance compared to a conventional designed system. In a conventional way, source coding and channel coding are designed to accomplish the best system performance respectively. With simply combining the best source coding scheme with the best channel coding scheme together, the system does not promise a better overall performance.
Consequently, the present algorithm employs joint source-channel coding scheme and MIMO concept to get the best performance in the system design over fading channel. We are interested in the joint source-channel coding with modulation scheme design under the channel capacity constraint consideration in a MIMO system. Figure 1 shows joint source-channel codes under the combination of various source coding rates and various channel coding rates. Source coding is concerned with the efficient representation of a signal. While bit errors in the uncompressed signal can cause minimal distortion, in its compressed format a single bit error can lead to significantly large errors. For data, channel coding is necessary to overcome the errors resulted from transmission channel. We have noticed that combining source coding with adequate channel coding, we should be able to achieve a better system performance. Assuming that the overall system transmission rate r = k/n, where k is the source coding rate and n is the channel coding rate. In Fig. 1, we have found that a better performance (with a lower distortion) can be promised when we increase the source coding rate k, while we increase the channel coding rate n, a higher bit error rate (a lower system performance) happened under the same Eb/N0, signal-to-noise ratio (SNR) criterion. Therefore, we would like to design a transmission system with higher source coding rate k but lower channel coding rate n to achieve a higher overall transmission rate r. Since the overall transmission rate r is under channel capacity limitation, we have to justify the concept with proper method to design transmission system.
The overall transmission rate r can be obtained by source coding rate k cooperated with channel coding rate n. We will not satisfy the system performance while we have a high source compression ratio (lower k) with strong channel protection (lower n). In turns, if we apply a low source compression ratio (higher source coding rate k with low distortion) but a high channel coding rate n (weak channel protection capability) to the system, which may result in higher bit error rate (BER) performance, we are not satisfactory with the reconstructed signal from the received high BER data. It is quite clear that we have to find a better match between source coding rate and channel coding rate to assure an acceptable system performance.
The most significant criterion in designing a transmission system is the channel capacity limitation. The available channel capacity restricts the overall transmission rate r, which is the rate between source coding rate k and channel coding rate n. We have to consider source coding rate, channel coding rate, and the corresponding modulation type all together simultaneously to cope with the channel capacity limitation. Assuming channel capacity limitation is one bit/transmission, we are asked to keep overall transmission rate r ≤ 1 bit/channel-use, which can be achieved only with k ≤ n. Therefore, we will keep our system rate design with r ≈ 1 and r ≤ 1, that is, k ≈ n and k ≤ n. Furthermore, space-time block coding (STBC) algorithm was introduced (Alamouti, 1998; Tarokh et al., 1999) as an effective transmit diversity technique to resist fading effect. For a fixed number of transmit antennas, its decoding complexity increases exponentially with the transmission rate. The proposed algorithm employs joint source-channel coding scheme with STBC technique to get the best performance in MIMO systems design.