Joint power control and source-channel coding for video communication over wireless networks

Video communication over wireless link is a challenging task due to the time-varying characteristics of a wireless channel and limited battery resource in the handheld devices. This paper proposes a power-optimized approach for video communication, which simultaneously controls the transmission power, source rate and error protection level to minimize the total power consumption for all users. The performance of the cellular CDMA system using our proposed scheme is compared with the one using a fixed power-control scheme. The simulation results show that our proposed joint power control and source-channel coding scheme achieves significant power saving compared to the fixed scheme. . INTRODUCTION Video over wireless networks has undergone enormous development recently, due to continuing growth of wireless communication. However, wireless video communication faces several challenges including bandwidth requirement and battery lifetime constraints. Minimizing average power consumption while keeping the quality of service (QoS) at mobile station (MS) is of great interest, because the next generation networks are to accommodate mobile users with portable and battery-powered equipment accessing to a wide array of information services. Power control and joint source-channel coding (JSCC) are two effective approaches to supporting quality of service (QoS) for robust video communication over wireless networks. Power control is performed from group point of view by controlling the transmission power and spreading gain (transmission rate) of a group of users. Most power control schemes are designed to maintain a constant Eb/N0 in the MS by decreasing the channel fading effect. The problem of power control and resource management has been discussed in [1-3], therein only transmission power is considered. On the other hand, JSCC is performed from individual user point of view by introducing redundancy to combat the transmission errors [4]. Most existing JSCC schemes are designed to minimize the distortion alone. To the best of our knowledge, the techniques of power control and JSCC have been studied separately to date. In this paper, we simultaneously controls transmission power, source rate and error protection level to minimize the power consumption of the MS. Meanwhile, the desired QoS for * This work is performed while Zhu Ji is a visiting student at Microsoft Research China. Zhu Ji and Jianhua Lu are from Department of E.E., Tsinghua University, Beijing. video transmission is maintained in a single-cell multi-user environment. . JOINT POWER CONTROL AND SOURCE-CHANNEL CODING In the video transmission scheme, the total power consumed in the MS consists of transmission power and processing power. Processing power is mainly determined by computational costs for source coding and channel coding. Transmission power, on the other hand, depends on the bit energy (εb) and total bit rate to deliver. Both transmission power and processing power should be controlled so as to adapt to the changing channel conditions. Reducing transmission power of a user will increase its battery lifetime, lower the interference to neighbors, and heighten bit error rate for its own transmission. Figure 1 illustrates our proposed scheme with joint power control and source-channel coding. Besides the closed-loop power control scheme in UMTS [5], we introduce a novel functionality block, power consumption minimization. In our scheme, outer-loop power control and inner-loop power control operate in parallel. The outer-loop is responsible for setting a target for signal-to-interference ratio (SIR) used by the inner-loop power control for each MS. This target is not only set on an individual basis for each MS according to the service requirement and channel protection level for each MS, but also affected by the feedbacks from the power consumption minimization blocks of all users in the cell. In addition, variable spreading factor (SF) is provided by the MS when performing rate control. Meanwhile, the inner-loop power control mechanism adjusts the MS transmit power in order to keep the received uplink Eb/N0 at the given Eb/N0 target. The base station (BS) compares the received Eb/N0 from the MS with the target Eb/N0 and creates a multistep transmit power control (TPC) command for each MS in every time-slot. Furthermore, the multistep TPC command could enable the MS to perform accurate long range channel prediction [6] and be aware of the average interference caused by other users in the same cell. Moreover, each MS may adjust its transmission power with the step size, which is obtained by simultaneously considering the predicted channel condition and minimizing the power consumed in source coding, channel coding and transmission. In addition, a pilot channel between the BS and each MS is used to transmit the multistep TPC command and average interference information to other users. In the meantime, the feedback is received to determine the target SIR and SF. The design of power-optimized video communication system for MS requires exploiting the tradeoff among data, redundancy, processing power, and transmission power according to the characteristics of time-varying channel. Based on the above consideration, we propose an architecture for power-minimized video communication over wireless channel, which is shown in Figure 2. The key components of the architecture include power-reconfigurable video encoder, UEP channel encoder, power amplifier, and network-aware power consumption optimizer (NAPCO).