Building a WiMAX System with Kaben’s Products and Technology
The WiMAX standard was initially introduced to address the “last mile” connectivity for fixed terminals; however, its mandate was subsequently expanded to also include mobile terminals carrying data intensive applications. By supporting voice services on these channels, WiMAX has also become one of the candidate standards for replacing the current GSM and CDMA cellular networks.
Each terminal in a WiMAX cell is allocated 256 sub-carriers (of which 200 are used for data), and can achieve a spectrum efficiency of up to 3.7 bits / Hz. The base-station can communicate with 8 terminals simultaneously, by transmitting and receiving 2048 equally spaced sub-carriers. In principal, a fixed terminal can support data up to 70 Mbps, while a mobile terminal can handle 10 Mbps at a 2 Km range in an urban environment.
Since WiMAX has evolved to become a common-carrier supported standard, its deployment is taking place in the licensed frequency bands, in particular in the 2.3 GHz, 2.5 GHz and 3.3 GHz bands, more so than in the unlicensed bands.
The radio front-end of the Phy layer for WiMAX has several major hurdles that must be dealt with. In addition to being tunable over the three bands mentioned above, it must be able to handle a large peak-to-average power ratio of more than 20 dB. 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 channel from the frequency band in use, while simultaneously suppressing other adjacent channel and alternate channel signals.
Kaben’s WiMAX front-end provides all functions between the RF Baluns and the digital Phy. 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 Digital-to-IF conversion with 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 256, closely spaced sub-carriers, and the band selection required by the WiMAX standard.
The receiver on-chip IF filter, and the transmitter on-chip Digital-to-IF converter are both realized using the Kaben sampling-IF technology. Through the use of Kaben’s sampling-IF filters, the receiver selects the desired band with no dispersion (frequency dependent phase variation), and with steep skirts to achieve an adjacent band rejection level of -60 dB. The sampling-IF technology also produces 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 WiMAX front-end provides unbeatable performance in terms of linearity, phase noise, and suppression of unwanted signals and spurs.
