Microwave Engineering Europe - April 2008 - (Page 32)

32 CMOS PAs cuts the power consumption of the user device and extends its battery life. Because the MMSE receiver requires fewer computations than the MLD receiver, under certain transmission conditions the performance difference between the MMSE receiver and MLD is negligible. We can measure and test the correlation condition of the MIMO channel before we decide which receiver should be used. If the MIMO channel correlation is very low or is orthogonal, the MMSE receiver can be used with no performance loss, while reducing the computation load by avoiding use of the MLD receiver. Similarly, we can use the MMSE receiver when the signal-to-noise ratio is high. The advanced receiver can be further extended by a successive interference cancellation (SIC) receiver architecture. The rationale behind the SIC receiver is that the signal quality of the multiple transmit data streams is not the same, because of the fading variations of the MIMO channel. We can successfully demodulate the ﬁrst data stream, remodulate it and then subtract the ﬁrst data stream from the receive input mixture, absent interference from the ﬁrst data stream. We can then demodulate the second data stream successfully with the simplest maximum ratio combining (MRC) receiver. Because of the nature of the MIMO channel, the eigen value of the MIMO channel matrix represents the signal strength for the data stream. For the two-transmit and two-receive MIMO conﬁguration, different modulations for the different data streams can be scheduled for transmission at the basestation. The user device measures the signal quality (typically one strong data stream and one weak data stream) and uses the feedback channel to request the coding modulations for each data stream transmitting from the basestation. If the user device possesses an SIC receiver, however, the signal-quality measurement can be based on the receiver operation procedure. In this case, the weak data stream’s signal quality is measured in the absence of interference from the strong data stream. Therefore, the user device can request the increased coding and modulation transmission level for the second data stream. This can improve the throughput of the second data stream, increasing the overall throughput of the user device. As the baseline signaling format for all 4G technologies, a MIMO receiver will be built into all 4G-capable devices. MIMO receivers can deliver superior performance and user experience as a common receiver engine using low-cost ASIC technology, able to be embedded into both WiMax and LTE devices of all form factors. The adaptive receiver structure can be leveraged to reduce power consumption and extend battery life. Wen Tong (wentong@nortel.com) is a Nortel fellow and leader of its wireless technology labs. He holds more than 52 patents. CMOS PAs pave the way for one-chip phones By David Kang, President of Engineering, Axiom Microdevices Inc. he cell phone market has become one of the most competitive arenas in the semiconductor industry, with manufacturers producing more than 1 billion units annually. The argument has been made that specialty processes, such as gallium arsenide (GaAs), laterally diffused MOS (LDMOS) or silicon germanium (SiGe) bipolar CMOS (BiCMOS), with less-precise geometries, may offer the short-term cost advantage and linear modulation demanded by manufacturers and designers. The economies of scale inherent in CMOS, T however, have driven the industry to make signiﬁcant investments in this process, creating volumes that have outlasted, and will continue to outlast, any niche process offerings. For example, transceiver blocks previously realized in specialty BiCMOS processes from vendors such as Inﬁneon, NXP and Skyworks have long since been implemented in CMOS – and, in some cases, integrated with the handset’s main processor inside a system-on-chip. Designers have repeatedly found that implementing an analog block in standard CMOS has paid off in the long run, despite the hurdles posed by challenging circuit blocks in a less-forgiving process. One area that the CMOS process has not been able to successfully penetrate, however, is the power ampliﬁer (PA) block, which remains a key element within the cell phone. Until now, the PA block has been developed using a specialty GaAs or LDMOS process coupled with a hybrid module packaging technology – in total an expensive manufacturing ﬂow, which has made the PA a substantial part of a cell phone’s bill of materials. The specialty Microwave Engineering Europe ● April 2008 ● www.mwee.com 030-031-032-033_MWEE.indd 32 27/03/08 15:57:53 http://www.mwee.com

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Microwave Engineering Europe - April 2008 News Contents Comment Test and Measurement: Comprehensive WiMAX and Wi-Fi Product Design Demands Effective Channel Emulation Military/Aerospace Focus: Hardware Needs Limit Software Radio Interview — Mitsubishi Electric Europe: GaAs Technologies Spanning High-End Space and Radar Through to Cost-Sensitive Handset and LNB Applications How Do You Test ZigBee Transmitters? Advanced Receiver Design Boosts Performance CMOS PAs Pave the Way for One-Chip Phones Products Calendar

Microwave Engineering Europe - April 2008

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