矢量广播信道下CDMA和TDMA信道容量的比较

对矢量广播信道下TDMA(time division multiple access)系统和CDMA(code division multiple access)系统的速率和容量(sum rate capacity)进行了研究。在TDMA系统中，每一时刻基站只能向一个用户发送信号，而CDMA则可以同时向所有的用户发送信号。对于TDMA系统，当信道是标量时，它可以达到速率和容量，而当基站带有多根天线时，TDMA的速率和容量就不是最优的。经过详细的分析，推导出了CDMA 系统在矢量广播信道下速率和容量的上界以及TDMA系统在矢量广播信道下速率和容量的下界。通过2个界的比较表明，在矢量广播信道下CDMA系统速率和最多是TDMA系统的min(M,K)倍，其中M是发射天线的数目，K是系统中的用户数目。

Capacity Comparison of CDMA and TDMA in Vector Broadcast Channel

The sum-rate capacity of slow fading vector broadcast channel in code division multiple access (CDMA) system and time division multiple access (TDMA) system are thoroughly researched. The base station can only transmit to one user at a time in TDMA system. However, in CDMA system, the base station can send data to all the users at the same time. The TDMA system can achieves the sum-rate capacity if the base station has only one transmit antenna, but it is sub-optimal when the base station has multiple antennas. By a detailed analysis, an upper bound of sum-rate capacity in CDMA system and a lower bound of sum-rate capacity in TDMA system are derived respectively. According to these two bounds, the sum-rate capacity ratio of CDMA to TDMA at most can achieve the minimum of M and K. Here M is the number of the transmit antennas and K is the number of the users in this vector broadcast channel.