Building a W-USB System with Kaben's Products and Technology The Wireless USB standard will provide high speed connectivity to a laptop, desk-top computer, or other consumer product, in a wireless manner. In specific, it will deliver up to 480 Mbps occupying a 528 MHz bandwidth, over distances up to 3 meters. The standard is based on the use of an OFDM (Orthogonal Frequency Division Multiplexed) signal structure having 100 data sub-carriers, 12 unmodulated pilot sub-carriers, and 10 unused guard sub-carriers. Fourteen separate bands are spaced over the frequency range from 3.16 GHz to 10.6 GHz, and are grouped into 4 band-groups having 3 bands each, and 1 band-group having 2 bands. Both frequency domain OFDM and time domain frequency hopping are used to spread the signal over a wide bandwidth.
The radio front-end of the Phy layer for the wireless USB has several major hurdles that must be dealt with. In addition to handling a large peak-to-average power ratio of more than 20 dB, the front-end must also handle a large instantaneous bandwidth of more than 500 MHz. As a result, the front-end must provide a high degree of linearity, both on transmit and on reception. It must also be able to correct for any frequency dependent, amplitude variations and phase change (dispersion), resulting from the wireless channel or from itself. The front end must be able to select the appropriate 528 MHz channel from the 7.5 GHz of available spectrum, while simultaneously suppressing other adjacent channel and alternate channel signals. Finally, the front-end must perform in the presence of other licensed and unlicensed signals occupying the band.
Kaben's wireless USB front-end provides all functions between the RF Baluns and the digital Phy level required by a wireless USB. For the receiver, this includes balun conversion, low noise amplification, heterodyne down-conversion, on-chip IF filtering and decimation, and baseband A/D conversion. For the transmitter, the Kaben front-end provides wide band, ultra linear DAC with baseband reconstruction filtering, direct to RF up-conversion, RF amplification and balun conversion.
Kaben's unique capability in high performance frequency synthesis is used for both the receiver down-conversion and the transmitter up-conversion, as well as for the sampling-RF clock generation. The low phase noise, low spur level, fast settling synthesizer achieves the purity required by the 128, closely spaced sub-carriers, and the band selection required by the wireless USB standard.
The receiver on-chip IF filter, and the transmitter on-chip DAC are both realized using the Kaben sampling-IF technology. Through the use of parallel, channelized sampling-IF filters, the receiver provides a bandwidth of 535 MHz with no dispersion (frequency dependent phase variation), steep skirts to an adjacent band rejection level of -60 dB, and a decimated (frequency down-converted) output to completely suppress clock and image feed through.
The wide bandwidth, large dynamic range (12 bits) transmitter Digital-to-IF converter provides an analog IF signal to the up-converter, uncompromised by sin x / x amplitude distortion, glitch energy corruption, or clock feed through.
Based on the extreme performances of these three unique technologies; the low phase noise / low spur level frequency synthesizer, the field programmable sampling-IF filters, and the wide band, high dynamic range, Digital-to-IF converter, the Kaben wireless USB front-end provides unbeatable performance in terms of linearity, phase noise, and suppression of unwanted signals and spurs.  |
