HSDPA Backhaul over Ethernet

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 peak per user, HSDPA can significantly shorten the time required to download rich-media files to an HSDPA handset. As an example, downloading one minute of audio from an MP3 music file is calculated to take 132 seconds with GPRS, 22.4 seconds with UMTS and only 4.1 seconds with HSDPA. The result is an 82% savings in air time. That means it is possible to serve more mobile subscribers using the same infrastructure. Such high capacity performance, however, comes at 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/SONET or ATM transmission services with E1/T1 access lines. Although 3G data traffic is still only a relatively small overall portion of mobile transmission, this situation is expected to change quickly as UMTS operators take their HSDPA networks onstream over the next few years. Assuming that additional E1/T1 lines are readily available (approximately 16 E1/T1s per Node B) from the landline operator, the amount of backhaul traffic is predicted to 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 deployment of IP DSLAMs on the one hand, and the successful implementation of pseudowire devices for cellular backhaul over DSL on the other, have combined to enable W-CDMA operators to consider the option of using lower-cost broadband networks in the backhaul.

Because packet-switched networks are not yet engineered to fully provide the same quality of service as TDM or ATM, an interim hybrid approach is being adopted that will guarantee voice quality while reducing access costs. The hybrid 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 the company's ACE-3200 Multiservice Cell-site Unit to aggregate 2G and 3G traffic. Voice and signaling are transmitted via standard E1/T1 lines, while HSDPA (and other broadband) data is extracted and, using pseudowire technology, backhauled via Ethernet services over DSL or Metro Ethernet networks.Voice is delivered over a minimum number of E1/T1 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 their revenues and profitability from rich-media 3G content.