HSDPA Hybrid Transport Solution

The introduction of HSDPA (high speed downlink packet access) is expected to enable mobile operators to exploit the full potential of 3G technology by offering mobile broadband services at competitive costs. With a maximum theoretical peak throughput of 14.4 Mbps per user, HSDPA can significantly reduce the time required to download rich-media files. Downloading one minute of audio from an MP3 music file, for example, takes 132 seconds with GPRS and 22.4 seconds with UMTS, but only 4.1 seconds with HSDPA. The result is an 82% savings in airtime, making it possible to serve more subscribers using the same infrastructure.

By delivering speeds comparable to or better than fixed-line broadband access systems, HSDPA promises to transform cellular telephony. But high capacity performance has a price: an exponential increase in the bandwidth required to backhaul cellular traffic from Node Bs to the RNC (radio network controller).
 
Today, the majority of cellular networks rely on SDH or ATM transmission services with E1 access lines from the base station or Node B to the base station controller (BSC) or RNC. Although 3G data traffic is still only a relatively small overall portion of mobile transmission, this situation will change quickly as UMTS operators take their HSDPA networks onstream. Assuming that additional E1 lines were readily available from the landline operator, traffic will grow faster than the expected average revenue per user (ARPU).

This situation is forcing mobile operators to seek alternative backhaul solutions that are cost effective and scalable and will not compromise the integrity of the voice quality. The steady increase in deployment of IP DSLAMs on the one hand, and the successful implementation of pseudowire devices for cellular backhaul over DSL on the other, sway UMTS operators to consider lower-cost broadband networks in the backhaul. As a first migration step towards packet-based transport, an interim hybrid approach is being adopted to guarantee voice quality while reducing access costs. That solution calls for the diversion of voice and real-time traffic to a TDM or ATM transport network while the HSDPA data can be carried over any packet transport media.

RAD’s hybrid transport solution for HSDPA traffic employs its ACE-3200 multiservice cell-site unit to aggregate 2G and 3G traffic. Voice and signaling are transmitted over E1 lines, while HSDPA (and other broadband) data is segregated and, using pseudowire technology, backhauled via Ethernet services over DSL or Metro Ethernet networks. Voice is delivered over a minimum number of E1 circuits to the TDM or ATM transport network. At the other end of the RAN, RAD’s ACE-3400 multiservice access concentrator routes 2G voice to the BSC, performs SDH-to-ATM conversion at the BSC and also tears down the pseudowire tunnel to transport the HSDPA data to the RNC.

By applying RAD’s HSDPA segregation solution using pseudowire technology, mobile operators can speedily deploy high capacity W-CDMA services, keeping HSDPA operating costs to a minimum while increasing revenue and profitability from rich-media 3G content.