HSPDA - the next step for 3G
Among the next-generation contenders in the ring are Flarion's Flash OFDM (F-OFDM), WiMAX (IEEE802.16e) and CDMA2000 1XEV-DO. But it's high-speed downlink packet access, or HSDPA, that enables a smooth, cost-efficient upgrade to existing W-CDMA networks at minimal cost.
HSDPA's incremental UMTS network upgrade aims to increase user peak data rates and quality-of-service and improve spectral efficiency - much like EDGE and 1XRTT have done for 2G. Although UMTS enables streaming video, broadband Internet access and video conferencing, HSDPA offers peak downlink data rates of up to 14 Mbps - dramatically more than the 384 kbps that is typical of today's UMTS and the highest data rate of any available mobile WAN technology.
HSPDA works by moving important processing functions closer to the air interface. Although current UMTS networks perform network scheduling and retransmission in the radio network controller, HSDPA moves these functions to the base station (called Node B in UMTS systems), allowing scheduling priority to take account of channel quality and terminal capabilities. Retransmission also benefits from hybrid automatic retransmission request in which retransmissions are combined with prior signal transmissions to improve overall reception. HSDPA adds a channel-sharing mechanism that allows several users to share the high-speed air interface channel and other technological advances such as adaptive modulation and coding, quadrature amplitude modulation and channel quality feedback. These enhancements allow HSDPA to roughly double the total throughput capacity of a network.
For consumers, that translates into shorter service response times, fewer waits and faster connections. Wireless users can talk on the phone while simultaneously downloading packet data. Most important, they can use their wireless handsets to download Web pages, audio or video at speeds well above the performance they are accustomed to with landline-based DSL or even cable Internet connections.
What's good for the consumer ultimately is good for the operator, provided the costs and barriers to deployment are not too great. HSDPA significantly enhances W-CDMA with little hardware investment. It operates in 5 MHz channels and is backward-compatible with current W-CDMA networks. This allows network operators to introduce greater capacity and higher data speeds on the same carriers as with existing Release '99 W-CDMA services. A system may be upgraded incrementally to enhance performance for users of the latest handsets without losing network capacity or interrupting service to subscribers who rely on older handset technology.
As an extension of GSM, HSDPA can be deployed readily in the United States, Europe and Japan. In fact, some service providers may introduce pilot projects within the next year. By 2007, HSDPA likely will be a leading technology worldwide. This means that operators will be able to offer global roaming capabilities based on infrastructure already in place today and serving a sizable handset base, including older W-CDMA units.
HSDPA's incremental upgrade and dramatic performance benefits will serve as the best stepping stone to 4G for many operators. Texas Instruments is working within the 3G Partnership Project (3GPP) to enhance the standard in ways that will provide continuing business opportunities for wireless operators.
Among the developments we see down the road is high-speed uplink packet access (HSUPA), which will augment HSDPA to create a more symmetrical high performance system. We also expect ongoing improvements to boost network efficiency, reduce latency and increase overall network throughput.
All of this can be achieved through incremental upgrades to time proven W-CDMA technology. The HSDPA standard has been in place for a couple of years. Base station equipment is now starting to reach the market and handsets will follow, with widespread deployment anticipated in 2006 and 2007.
For consumers, HSDPA will help 3G technology fulfill its promise with more sophisticated data applications and better performance. For operators, this technology enables a highly competitive network with only incremental enhancements to existing infrastructure. HSDPA promises to provide a better return on investment and stronger revenues per megabit delivered compared to other avenues to very high-speed service.
Bill Krenik is manager of wireless advanced architectures in the Wireless Terminals Business Unit at Texas Instruments.
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