1.3 Transceivers for wireless and mobile communications

As discussed above, transceivers play a key role in the successful applications of wireless communication, networking, accessing and connecting. Apart from these well-known application areas, transceivers have also been widely used in many other applications such as backplane, ambient intelligence, and embedded systems. Actually, transceivers will become an essential device in any future intelligent electronic system as wireless connectivity becomes more and more popular.

Today's transceivers are tending towards single-chip CMOS devices with very small physical size, very low power consumption and very low cost. SoC transceivers involve a mixed-signal design containing both analogue and digital circuits. Integration of the RF frontend and channel filters of a transceiver is particularly challenging. Although great progress has been made, real single-chip transceivers having everything on one chip are not commonplace.

Recently, multimode transceivers for Bluetooth and 802.11, or GSM, IMT2000 and UMTS have been receiving particular attention. Now, universal transceivers for all types of application including local networking, home connectivity, and cellular communications are also being pursued. Reconfigurability, programmability and tunability are a must in such transceivers. In these transceivers, the operating frequency may be variable and the channel bandwidth may be variable to accommodate different mobile and wireless standards. The carrier frequency, for example, is typically within the range 1–5 GHz. The major design challenges over variable carrier frequencies and bandwidths are transceiver filtering and linearity. Future transceiver design must also consider requirements of smart antennas and ultra-wideband radio.

Software and DSP-based concepts have been hot topics in so-called softwaredefined radio (SDR). There are some very tough challenges for use of SDR in high-performance long-range wireless communications. Firstly, the spectrum allocated to 3G is above 2 GHz. At such carrier frequencies the pure software radio approach will for some time remain impractical, since analogue-to-digital conversion at such carrier frequencies remains some way in the future. Secondly, the complexity of the 3G air interfaces requires significantly greater processing than second-generation systems. This precludes low-power terminals using traditional DSP devices. Realistically, direct conversion at the antenna in handsets will not be feasible for many years. Even for GSM standards there is still some way to go towards pure software radio. On the other hand, for low performance requirements in short-range wireless connectivity applications such as Bluetooth, complex DSP techniques may not be a high priority. In such applications, low cost, low power, and small-size implementation is more important; therefore RF IC may be more crucial than DSP. The fact is that no matter how fast DSP is, the power consumption tends to be simply too high for many portable applications. How far DSP can be pushed towards the antenna is not just up to the DSP technology itself, but is also dependent on advances in the analogue part of the system including the analogue-to-digital converter (ADC). There is a trade-off between high performance multifunctionality and single-chip integratability for transceivers. In this book we try to obtain practical solutions for optimum transceiver design in the RF and analogue domains.