Abstract: 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 detailedanalysis, 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.

Key words: vector broadcast channel, sumrate capacity, code division multiple access