Dynamic Performance of a Chip Level Adaptive Equalizer in a UMTS High Speed Downlink Packet Access (HSDPA) Terminal

The HSDPA mode of the 3GPP UMTS FDD standard extends the peak downlink rate of the W-CDMA waveform to 14 Mbps. To achieve high rates across a multipath channel the demodulator must include an advanced receiver rather than a conventional Rake. This paper presents the performance of an NLMS-based adaptive equalizer that supports mobile velocities as high as 250 km/h. The equalizer works with radio and implementation impairments typical of a non-HSDPA receiver, so redesign of the terminal front end is not required. A key aspect of the design is dynamically adjusting the equalizer step size and leakage parameter. There is often concern about the ability of an adaptive algorithm to operate in a highly mobile environment. The transient behavior is discussed in the context of HSDPA operation and examples are provided of initial convergence and operation after a sudden change in propagation conditions.