The Bitrate Limits of HSPA+ Enhanced Uplink

In 2009 mobile broadband is living its success story and demand for higher data rates is growing constantly. More advanced HSPA technologies have been released recently by manufacturers, and many operators have multiplied their offered downlink peak rates. In the uplink however, there has not been as much buzz around the new technologies lately. This is somewhat natural as traditional mobile traffic is highly asymmetric and weighted towards downlink. Downlink data rates are therefore the quantity most users and operator marketing departments are interested in. However, the uplink should not be forgotten as it can have big impact on the performance of both today’s and future mobile services. User perceived performance of services such as web-browsing also depends on delays of request messages in uplink direction, and the delays are mandated by achievable uplink user data rates and latencies. Also overall uplink system capacity becomes an issue as mobile broadband usage increases significantly. Additionally, as traffic-symmetric services such as file sharing, social media and user generated content are becoming more popular, it can be foreseen that the uplink data rate becomes more relevant KPI in the future.

3GPP new releases promise high peak rates with Enhanced Uplink (EUL). There are however some major radio resource limitations for data rates, unique to the uplink direction. In this paper we present an analysis of the limitations of uplink data rates in current and future WCDMA networks.

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