Preparations beyond HSDPA

05 Mar 2007

With 3G failing to deliver on the data side with its promises of 2-Mbps data rates, W-CMDA operators needed a fix to their R99 (Release 99) systems and needed it fast. Not only was there the pressure of cdma2000 operators taking business away, there was (and still is) the pressure felt from the impending launch of WiMAX systems, also providing broadband data rates.

The answer from 3GPP was Release 5 featuring HSDPA, which offers several significant improvements for R99 networks, and network operators pushed for its implementation before the ink on the Release 5 specification was barely dry. Furthermore, the operators are now pushing for the uplink portion of the fix, Release 6, featuring HSUPA (high speed uplink packet access).
HSDPA is tagged as being a software update. But this is just like Microsoft's Vista OS being just a software update. Many operators will find that if their network isn't 'HSDPA ready', then they will need to update/expand the hardware capabilities to be able to handle the added data volume.

Testing will be more than a software update as well. When integrating system components or load testing HSDPA/HSUPA-capable UTRAN devices, manufacturers and operators alike will face an increase in the data traffic to be analyzed by one order of magnitude compared to R99-based systems.

But independent of whether adding HSDPA is merely a software update or a software/hardware update, the benefits for the operators are several fold. The headline spec for HSDPA is that it will support peak data rates of 14.4 Mbps in one cell, e.g., nine video clips can be sent via HSDPA in the same time required to send one on R99. While realistic data rates for HSDPA may actually only be a few megabits per second or less, the actual quantity and number of users achieved in a cell will improve significantly over R99 networks.

For example, instead of limiting high-speed data access to fewer than five users in a cell, HSDPA can deliver 384-kbps rates to up to possibly 30 users. However, test engineers need to be careful to not treat HSDPA as just a faster Release 99. There are key differences between the two, and these differences need to be considered closely.

As its name implies, HSDPA is meant for downlink data traffic only. For uplink data traffic improvement, HSDPA is needed to bump up the maximum theoretical data rate to 5.6 Mbps. HSUPA gains much of its data-rate improvement by defining a new transport channel - E-DCH (enhanced dedicated channel). Though adding HSDPA capability to a network creates more than a few testing challenges, adding HSUPA will not impact testing requirement as severely.

Testing the testers

The introduction of HSPA, i.e., the common operation of HSDPA and HSUPA, is not the last step in the evolution chain, however. WiMAX and other technologies are keeping the pressure on for further improvements. In response, 3GPP is developing a specification labeled UTS LTE (UMTS long-term evolution) with the improvements required to keep network operators competitive for applications such as broadband mobile radio or mobile TV. The UMTS LTE specification is not scheduled to be finalized until September 2007; however, it is now stable enough for designers to begin work on system components.

UMTS LTE's goal is to achieve data rates of up to 100 Mbps in the downlink (an increase in capacity of three to five times compared with HSDPA in the same bandwidth) and up to 50 Mbps in the uplink. Like WiMAX, UMTS LTE will use OFDMA (orthogonal frequency division multiple access) technology for the downlink. This switch from W-CDMA to OFDMA will be a big change at the very lowest level of the radio communications portion of a system and achieving synchronization will be a major challenge. For the uplink, UMTS LTE will use SC-FDMA (single carrier frequency division multiple access technology). Plus UMTS LTE is adding MIMO antenna technology to the mix.

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