The Cambridge, UK-based company is targeting the DECT phone replacement market with its UniVox reference design, said Simon Finch, VP of its WiFi strategic business unit. However, work is also underway to port its underlying UniFi silicon technology to the ARM processors in cellphones, in orer to enable dual-mode cellular/WiFi phones with the power-efficient features of the CSR chipsets.
The challenge faced in using WiFi infrastructure for voice traffic on untethered phones, whether cellular or merely cordless, is power consumption.
Whereas most of our competitors come from a PC background, where the presence of a lithium ion battery is the norm, we used our Bluetooth pedigree, with the knowledge that entailed in terms of power constraints, to launch our UniFi chipset for WiFi in November 2004, Finch said.
Limiting power consumption on WiFi phones requires two skillsets, he explained. On the one hand, there is the requirement to minimize the power needed for phones to remain on so as to receive calls. This can be achieved through so-called low-power listening, in which the device is in sleep mode, waking up to receive a beacon emitted by a WiFi access point (AP) every 100 milliseconds.
If there is no incoming call, it can go straight back to sleep, Finch said.
CSR and its competitors all use this technology, running their chips on slow clocks to enable this waking up function, but CSR claims greater efficiency already compared to other vendors, as well as promising a further halving of the time the chipset remains awake from early next year, with the next rev of its firmware.
The second requirement is for WiFi phones to be more energy efficient while a call is underway. In this scenario, the issue is that the phone must be on to receive VoIP packets, whose timing and frequency cannot be predicted. However, we now can put the chipset to sleep between incoming VoIP packets, Finch said, adding that this capability is the subject of an extension to the IEEE’s 802.11e standard for QoS in WiFi networks.
The extension, which was formulated by the 3GPP group, is called WMM-PS and requires technology in the APs, though we also have some proprietary technology to reduce power consumption in traditional, non-WMM APs to almost the same level, said Finch.
He explained that, whereas in a traditional WiFi network a phone would consumer around 270 milliWatts of power, with WMM-PS that can be reduced to 23.4 mW, while CSR’s proprietary technology to achieve the same end in non-WMM APs gets down to between 23 mW abd 30mW.
This translates, in terms of user benefits, to talk time of 20 hours with a full battery and 400 hours on standby. The UniVox reference design comprises everything from the schematics and layout through to the bill of materials (BOM) and a design tool for an ODM to customize the Man-Machine Interface (MMI).
CSR is talking about a complete BOM in the sub-$20 range, enabling it to target ODMs who are going after the low end of the market for cordless home phones, or what Finch called DECT replacement, referring to the Digital Enhanced Cordless Telecommunications standard designed for small areas and large numbers of users.
CSR’s main competitors in silicon for WiFi phones – as distinct from WiFi chipsets for PCs and laptops – are Marvell and Conexant, which has a collaboration with Franco-Italian vendor ST Micro.
