Build the optimal next-generation residential gateway

With the advent of the triple-play era (voice, video, and data), today's network operators are facing an increasing need for technology that lets them offer their customers end-to-end services along with quality of service (QoS). The wireless LAN residential gateway is already playing a critical role in service providers' quest to serve and retain customers as they adopt new service models.

Operators are in pursuit of residential gateway technology that lets consumers connect as many devices as possible throughout the home. Such devices give operators the leverage they need to bundle services and allow them to control services from the infrastructure to the premises to the end points, all the way inside the networked home (Fig. 1).

1. The proper bulding blocks of a residential gateway include both hardware and software layers.

WLAN devices based on the 802.11 standard are becoming the de-facto standard for residential gateways among end users installing home networks. There are several reasons why 802.11-based WLAN residential gateways are the preferred home networking devices over other wired or wireless alternatives such as Ethernet, HPNA, HomePlug, Ultra Wideband (UWB), and Bluetooth. The primary reason is that they use unlicensed spectrum and standard 802.11 technology. They also have the ability to address important issues such as network reach, end-to-end service management and QoS.

DSL-based gateways
DSL is expected to continue to outpace cable modem or WiMAX service as the most popular broadband service worldwide. Most DSL customers will choose WLAN residential gateways to network the CPE in their homes. According to the DSL Forum, there will be more than 107 million worldwide DSL subscribers by the end of this year's first quarter, with 10 million of those being added in that quarter.

Manufacturers of DSL-based WLAN gateways must overcome several challenges to capitalize on this growing market, which is rapidly migrating to a single-box solution. These issues include:

• Rate/range: devices must provide comprehensive coverage inside the house and deliver high throughput data rates to devices located at any distance from the gateway.
• Interference/cross talk: with the number of wireless devices rising, there's more opportunity for congestion-related problems.
• Future proofing: devices must be able to support emerging services, such as VoIP and video.
• Security/network management: devices must be easy to use, secure, and enable service providers to help user's troubleshoot problems at the customer premises.
• Power emission: gateways should be universal solutions that meet worldwide power standards.
• Cost efficiency.

Though this list of challenges is long, equipment designers and manufacturers are developing hardware and software techniques to resolve them. However, the techniques they use must not add cost to the bottom line of the WLAN gateway or add too much complexity to the manufacturing process.

Peak performance
One area of special concern related to hardware issues is RF performance, which impacts data rates and the gateway's reach. If RF performance is sub-par, dead spots in the home network can be a problem. Fortunately, several techniques address hardware-related RF performance issues affecting the device's rate and range. Properly applied, these techniques enable WLAN residential gateways to deliver whole-house coverage that's optimized for multiple devices in a congested networking environment.

A technique used to improve RF performance is increasing the output power and improving the sensitivity of the radio. However, note that each country sets limits on how much power unlicensed radios can use. For example, up to 30-dBm output power is allowed in the U.S. An optimal solution would be to increase the WLAN signals' output power while increasing the signal sensitivity of WLAN equipment. Both factors can dramatically effect the gateway's range. However, special care must be taken to ensure that these solutions don't add cost or complexity to the device. With forethought and innovation at the system design level, the challenges to extend the range by increasing transmit output power and receiver sensitivity can be achieved.

Other techniques such as beam steering or smart antenna design can also address the issues of rate, range, and elimination of dead spots, but both techniques require software and hardware support. The expense of designing these technologies into the gateway and certifying them could be a challenge. 802.11n, the developing standard for increasing data rates, addresses these issues using smart antenna technologies. However, the standard isn't ratified, and the market needs DSL-based residential gateways ASAP.

Noise also can decrease RF performance. In residential gateways, noise coupling is more likely because of high-speed interfaces such as Ethernet and DSL PHY, or a serial or parallel interface between the WLAN subsystem and the DSL subsystem on the board. To combat the problem, noise sources to the RF must be isolated and shielded from the rest of the board. A robust RF architecture and smart layout can prevent noise coupling problems.

Interference is another hardware-related obstacle that WLAN residential gateway designers face. A problem that impacts WLAN technology in general is the more 802.11-based devices operating in close proximity to one another, the more opportunity there is for them to interfere with each other. Even wireless devices that aren't trying to access the gateway, such as garage door openers, microwave, ovens or devices that use Bluetooth can cause interference. And as the 2.4-GHz band becomes more crowded, interference will become a greater threat to 802.11g performance. The situation is exacerbated by the fact that 802.11g OFDM receivers are more vulnerable to interference than 802.11b receivers.