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High Speed Downlink Packet Access (HSDPA) is a Third Generation Partnership Project (3GPP™) Release 5 standard that promises to make Wideband CDMA (WCDMA) networks faster and smarter. With HSDPA, operators can expect to increase capacity, offer richer multimedia services and start getting their money's worth out of 3G.

Why Does the Market Need HSDPA?
HSDPA maximizes network operator investments in 3G. It provides the bandwidth for advanced applications and a mobile alternative to broadband DSL and cable, while reducing the cost per megabyte of data transmission for the cellular operator.

Network operators in Europe, Japan and US are moving existing and new customers onto 3G networks as quickly as possible. There are two overarching reasons for this migration: capacity and value-added services. By increasing capacity, operators can accommodate more customers. This leads to increased revenue, a larger customer base to sell services to and greater return on investment.

As 3G networks are more spectrally efficient than 2G networks, operators can serve a greater number of standard voice customers. Transitioning to 3G networks also allows a greater variety of value added data services such as access to e-mail and e-mail attachments, video telephony, web browsing, music and video downloads. This extra bandwidth will accommodate more standard voice customers and provide the capacity for higher bandwidth data services-especially important as e-mail becomes more widely available on lower-tier mobile terminals. Without an enhancement such as HSDPA, capacity will become scarce.

This added capacity and efficiency can also benefit carriers' average revenue per user or per unit (ARPU) by increasing both the potential number of voice subscribers and the potential enhanced media services that carriers can sell to those subscribers. That additional ARPU can help carriers offset the costs of subsidizing new 3G phones for their customers.

Applications Rule!
Mobile users will work and play in a multicall environment. For instance, they might download videos or e-mail attachments, use location-based services or check data across a wireless network simultaneously, at higher resolutions, while playing a mobile game or participating in a conference call. As the transport user rate increases through HSDPA categories, more complex applications and a richer user experience are possible.

Mobile platform vendors should therefore focus on developing multicall HSDPA solutions. Some of the mobile platforms today support from up to 3.6 Mbps to 7.2 Mbps HSDPA throughput, making HSDPA services a reality. However, these multicall experiences can tax the applications processing power and battery life of a mobile device.

Mobile platforms for HSDPA services should therefore not only be high performance but also have built-in power management features that can extend battery life even when a user is multitasking. Technology that combines temperature sensing, voltage regulation and on-the-fly frequency adjustment to manage power efficiently can help 3G chipsets provide performance that is equal to or better than a processor that has a higher clock speed. In an average processor, higher clock speed means greater battery drain-so being able to provide the same performance at lower clock speeds is a power advantage.

Engineered for Mobility
The first HSDPA devices on the market have been PCMCIA cards in laptops. However, the market will quickly shift to devices with more mobility, such as smartphones, entertainment phones and video phones. As over-the-air data transfer speeds increase, emerging standards such as Multimedia Broadcast Multicast Subsystem (MBMS) and IP Multimedia Subsystem (IMS) will enable broader penetration of mobile services such as push-to-share, presence-based services (instant messaging) and mobile television.

According to industry sources, service providers have launched a total of 100 W-CDMA networks in 42 countries around the world with many of them announcing plans to further evolve their networks with HSDPA trials and service deployments in the near future. To achieve this goal, they want leading-edge HSDPA solutions that can deliver an enhanced user experience for such revenue- generating applications as real-time audio and streaming video, interactive gaming, Internet browsing and push-to-talk services.

To deliver on the promise of mobile broadband, HSDPA solutions should offer an optimal balance of power, speed, performance and cost. As mobility gains significance, miniaturization and size also become critical factors. Platforms especially well-suited for HSDPA mobile handsets reduce component count without sacrificing speed or power.

Flexibility is Key
Since HSDPA is a recent technology, flexible solutions are required. For instance, the mobile platform that can support open operating systems -especially important in mid-tier mobile devices-without a discrete applications processor and without requiring a third processor and a second memory system, would save board space and processing power. With this approach, there is no need to turn on the integrated MCU core for a data call, which saves power over alternative solutions that must run upper layers of stacks in the MCU core. The separation between the communications engine software (modem core) and the applications software (application core), a simpler software architecture therefore results in shorter software development times. Such an approach hits an optimal balance of power and cost.

Reduced time to market can favorably impact cost. This requires some flexibility while developing the solution. Flexible hardware which is supported by software that can configure the hardware in many different ways in effect shortens time to market. This is shorter than a dedicated hardware solution, because performance can be modified through software. Platform vendors should explore new generations of technology (i.e. modems) that can carry applications forward along an evolutionary path. This could reduce time to market for consumer products by 6-9 months for each new technology (i.e. 3.5G, 4G, 4.5G, etc)

Onward to HSUPA
At present HSDPA is capable of 3.6 Mbps speed and HSUPA is setting standards for 10 Mbps chipsets in the near future, followed closely by 14 Mbps chipsets.

Jointly, downlink and uplink enhancements are referred to as HSPA (High Speed Packet Access) services. Increased downlink and uplink speeds will further enhance user experiences and increase the use of application and activities especially where data is shared between users, for example interactive multi-player games.

High Speed Uplink Packet Access (HSUPA) is the next step, expected in 2007-2008. As the name implies, HSUPA is engineered to improve the spectral efficiency and latency for the WCDMA uplink. HSUPA will help improve symmetric applications such as videoconferencing, e-mailing large files back and forth, and transferring files. It is expected that HSUPA will use HSDPA's techniques to improve network efficiency, signal speed and quality.

Phil Tottle
The author is Senior Systems Engineer, Freescale Semiconductor
vadmail@cybermedia.co.in

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