Abstract
In this thesis, we investigate real-time interference measurement techniques for the 3rd generation wireless communication Wideband CDMA networks. The WCDMA system has versatile services with different data rates corresponding to different channel qualities. Obviously, a real-time channel quality measurement technique is the key to the success of effectively providing the wireless multimedia services in the WCDMA system.The basic idea of interference measurement comes from solving the signal-to-interference ratio (SIR) estimation problem. Several SIR estimation methods have been proposed for TDMA and CDMA cellular systems. We extend a low complexity method called interference projection, which was originally proposed for TDMA system, to CDMA system under a frequency-selective fading channel environment. However, the method requires different training sequences for different users. Since there is no obvious so-called training sequence in CDMA system, a possible solution is to use different patterns of pilot bits to replace the training sequences. Nevertheless, there are only very few pilot patterns in the WCDMA system, this solution may not be feasible to support a large number of users. Besides, using pilot bits for measuring the interference is difficult to achieve the goal of real-time measurement because signals are processed at the symbol level.To make it more practically and meet the demand of in-service real-time measuring, we proposed an innovative chip-based interference measurement technique. The key concept of this proposed method is to use the different subscribers’different spreading codes to replace the training sequences in the interference projection method. There are two major advantages for this solution. First, all the users’spreading codes are different and known only to the receiver for the user of interest. Second, since the signals are processed at chip-level, it is possible for the measurement to converge within a certain number of chip durations thereby achieving the goal of real-time measurement.We evaluate the chip-based interference measurement technique in the frequency-selective fading channel for the Wideband CDMA system. For both uplink and downlink cases, we apply our algorithms under different combination of spreading and scrambling codes. It will be demonstrated that the proposed methods can obtain the interference measurement within 0.1 msec with an average percentage error less than 5%. Therefore, we can easily achieve the requirement of estimating the SIR for every 0.667 msec time slot specified in the Wideband CDMA system.As a result, by employing the proposed chip-based interference measurement, many radio resource management algorithms, such as rate adaptation, power control, handover, and so on, can be enhanced to the slot-by-slot based adaptation algorithms to take advantage of better knowledge of channel quality. Hence, it can be expected that the proposed chip-based interference measurement technique will be possible to play a key role to fulfill the dream of high speed wireless multimedia communications in the future.