An important feature of HSDPA (high speed downlink packet access) for WCDMA is to provide very high data rates, up to several Mb/s in the downlink. In order to achieve these high data rates, a good receiver design is needed. Further, from a terminal perspective, the receiver design needs to be efficient from a cost, current and size perspective. A direct conversion receiver fulfills these criteria. However, such a receiver design often suffers from DC-offset and I/Q gain and phase mismatch, degrading the receiver performance. In this paper we make an analysis of how such impairments affect the performance in HSDPA. It is furthermore shown in the paper that by doing a good receiver design the implementation losses due to direct conversion impairments can be made small providing a possibility to make cost efficient HSDPA terminals with good receiver performance.

Direct conversion receivers are increasingly popular for use in mobile terminals. This is due to advantages over other architectures such as heterodyne receivers in terms of cost, electrical current, and physical size. However, a direct conversion receiver often generates a DC-offset that has to be taken care of either by suppressing the DC-offset in the radio-frequency part of the receiver, or by taking care of it during baseband processing. A theoretical analysis of the bit error rate (BER) performance in a direct conversion receiver with different levels of DC-offset suppression is presented. Explicit results are presented on how the BER depends on the signal-to-noise ratio (SNR), the signal-to-DC-level, and the choice of pilot symbols both with M-QAM and M-PSK in a slow, flat Rayleigh fading channel. A design rule, which applies to the design of DC-compensation in direct conversion receivers, is also presented.

It is essential to find suitable modes (combinations of alphabet sizes and code rates) for transmission in cellular systems. Bad choices result in low spectrum efficiency. An analytical method is proposed to find the modes which give the highest spectrum efficiency when using adaptive modulation. It is demonstrated that data rates considerably higher than 271 and 384 kbps are feasible in GSM and EDGE systems by using adaptive modulation. It is further demonstrated that the spectrum efficiency can be improved more than 100% by using three modes in a GSM system.