Keep it flexible, keep it fast

Flexible and upgradable network access techniques based on an IP approach could help wireless systems solve the access-speed challenge.

In today's fiercely competitive telecom market, wireless technologies must continually push the boundaries to keep up with hikes in wireline speed, where 8Mb/s access is now being offered to the domestic market at a very competitive price. Flexible and upgradable network-access techniques based on an IP approach may offer a solution.

A further challenge is the need to ensure a basic level of interoperability between multiple mobile technologies and standards, as well as achieving some degree of component and subsystem reusability. With constant pressure to upgrade networks for higher throughput, systems thus need a measure of "future-proofing." Software upgradability seems to be the answer on this front. In this article, we propose a network-access solution for equipment manufacturers looking to future-proof products to keep up with the volatile mobile data environment.

Wireless roadmap

We've seen rapid and dynamic progress made on the mobile-technology landscape—from GSM via GPRS and EDGE to 3G and now High Speed Downlink Packet Access (HSDPA) as an enhancement to 3G. The latter offers megabit-per-second download speeds to the user over a true packet data connection. And with its uplink counterpart HSUPA, it can satisfy most immediate mobile-data needs.

Nevertheless, the cost of entry for 3G operators has been huge, evidenced by high charges to the user. There are also limited opportunities for new operators to join. Consequently, WiMAX, which employs a multiple-access technique that uses orthogonal frequency channels rather than wideband spreading codes, is proving an attractive alternative.

Network-access challenge

Another clash of technologies is rippling through the wireline industry. It concerns the reliable transfer of voice and data signals to and from businesses and homes worldwide. The main shift has been from the original circuit-switched networks used for voice to the packet-switched networks for data and the Internet. Here, talk surrounds asynchronous transfer mode (ATM) and, increasingly, Internet Protocol (IP).

While wireline telcos meet the requirements for wider bandwidths and improved quality of service in this way, the mobile network infrastructure is just starting the migration. Driven by the push for wireless broadband applications, the backhaul interfaces need upgrading. For example, adding HSDPA to a basestation will multiply the number of required E1/T1 links by four or more.

Therefore, making the right interface choice means balancing the investment in legacy equipment with the need to upgrade and keep pace with the wireline broadband data market. Other issues, such as end-to-end security, latency, and synchronisation, are being addressed by the standardisation bodies as they consider IP.

Enhancements to wireless standards to improve spectrum usage entail either installing more basestations or equipping existing basestations with more advanced technology, such as multiple-input multiple-output (MIMO) antenna capability. However, both routes ultimately add cost to the infrastructure. In addition, providing adequate network access requires more access points that support wider bandwidths, and using smaller outdoor and indoor basestations requires the use of various backhaul technologies.

The Wintegra WinPath access packet processor was developed in direct response to these challenges. Introduced in 2001, its programmable architecture was different because its scope wasn't limited to the leading network interface standards of the day. The cornerstone device is the WinComm network processor, also known as the Packet Processing Engine. This supports all on-chip datapath software and implements most of the Layer 2 and 3 protocol processing.

As a processor, WinComm's programmability makes it possible to support custom protocols. It's surrounded by dedicated silicon for direct interfacing to most common access-equipment physical standards. For WAN applications, these include multiple T1/E1, T3/E3, Fast/Gigabit Ethernet OC3/OC12 ATM and POS, and VC12 channelised interfaces.

Such programmability and choice of interface means that any supported protocol can be selected independently as a transport mechanism on a per-port basis. Likewise, any port can switch to a new protocol without any hardware changes. Interworking between protocols is also a reality, and as technology moves from ATM to IP, a clear upgrade path is available.

To support the network processor, WinPath includes controllers for interfacing with external memory, such as SRAM, SDRAM, and Flash, along with standard functions and interfaces for timers, interrupts, UART, and I2C. For control-path processing, the device communicates directly with an external PowerPC, but also includes an optional embedded MIPS communications processor. This dual-processor architecture removes the need for external interfaces, allowing WinPath to take on more than the network access functionality.

Basestation cards

Shown is an Advanced Mezzanine Card (AMC) platform for an A-TCA line card that has been developed using WinPath (Fig. 1). The card is highly programmable, allowing a flexible and reconfigurable backhaul (Fig. 2). In smaller basestation applications, such as indoor picocells, WinPath can be used as part of a single-board, low-cost solution (Fig. 3). This additional network-interface flexibility allows basestations to be daisy-chained, with WinPath as both the master and downstream slave interfaces.

From a software perspective, WinPath provides classification, scheduling, and management of the backhaul interface, as well as the multiplexing and demultiplexing of multiple traffic streams to the baseband DSPs. Further flexibility includes support for Media Access Control (MAC) layer processing as well as schedulers for both HSDPA/HSUPA and WiMAX.

In addition to the usual benefits of increased integration, the programmability of WinPath provides support for different network-access interfaces. In addition, software enhancements to the wireless interface to allow for standards migration or product feature upgrades.

Main drivers in the broadband data market are increasing data rates and price pressure due to more intense competition. Bandwidth limitations in wireless mean that it will fall short of wireline performance. Consumers want data mobility, though, and operators are keen to exploit it to offset falling voice revenues.

Network infrastructure and the basestation interfaces are key to their ability to handle increased data traffic. A "standards-agnostic" solution like WinPath, where the datapath protocols are implemented in software, leads to lower cost and reduced power consumption. On the other hand, the programmability allows manufacturers to keep pace with changing standards without hardware upgrades.

Colin Alexander is director of wireless marketing at Wintegra Ltd., Blantyre, Glasgow, United Kingdom.

TAGS: Mobile
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