3G Handset and Network Design

The signal, transmitted by the Node B or handset, will usually travel along several different paths to reach the receiver. This is due to the reflective and refractive surfaces that are encountered by the propagating signal. Because the multiple paths ... [full story]

The digital receiver consists of a digital local oscillator, digital mixer, and a decimating lowpass filter. Digital samples from the ADC are split into two paths and applied to a pair of digital mixers. The mixers have digital local oscillator ... [full story]

As we have outlined in Chapter 2, there is a choice of superhet or zero/near-zero IF receiver architecture. If the superhet approach is chosen, it will certainly employ a sampled/ digitized IF approach in order to provide the functional flexibility ... [full story]

All the decorrelation processes rely on coded channel streams being visible at the demodulator at similar received power levels (energy per bit) ideally within 1 dB of each other. For every slot, the handset has to obtain channel estimates from ... [full story]

Because the handset operates in a very power restrictive environment, all stages must be optimized not only for signal performance but also power efficiency. Following the RRC filtering, the signal must be modulated onto an IF and up-converted to the ... [full story]

We have now generated a source coded, 3.84 Mcps, I and Q streamed, HPSK formatted signal. Although the bandwidth occupancy of the signal is directly a function of the 3.84 Mcps spreading code, the signal will contain higher frequency components ... [full story]

Figure 3.6 shows how the OVSF codes and scrambling codes are applied on the transmit side and then used to decorrelate the signal energy of interest on the receive side, having been processed through a root raised cosine (RRC) filter. ... [full story]

The second class of downlink physical channel is the Dedicated CHannel (DCH). The DCH is the mechanism through which specific user (handset) information (control + data) is conveyed. The DCH is used in both the downlink and uplink, although the ... [full story]

The SCH consists of two channels: the primary SCH and the secondary SCH (see Figure 3.4). These are used to enable the mobile to synchronize to the network in order for the mobile to identify the base station-specific scrambling code. ... [full story]

The downlink (Node B to handset) consists of a number of physical channels. One class (or group) of physical channels is the Common Control Physical CHannel (CCPCH). Information carried on the CCPCH is common to all handsets within a cell ... [full story]

The rule set for the code tree is that if a user is, for example, allocated code 8.0, no users are allowed to occupy any of the codes to the right, since they would not be orthogonal. A“fat” (480 kbps) ... [full story]

Spreading codes are designed to be orthogonal. In a perfectly synchronous transmission, multiple codes co-sharing an RF channel will have no cross-code correlation; that is, they will exhibit perfect distance. The disadvantage with orthogonal codes is that they are limited ... [full story]

Direct-Sequence Spread Spectrum (DSSS) techniques create a wide RF bandwidth signal by multiplying the user data and control data with digital spreading codes. The wideband characteristics are used in 3G systems to help overcome propagation distortions. As all users share ... [full story]

The general idea of a 3G air interface—IMT2000DS, TC, or MC—is to move the process of delivering sensitivity, selectivity, and stability from RF to baseband, saving on RF component count, RF component complexity, and cost, and increasing the channel selectivity ... [full story]

In the two previous chapters we identified that one of the principal design objectives in a cellular phone is to reduce component count, component complexity, and cost, and at the same time improve functionality. By functionality we mean dynamic range—that ... [full story]

Consider that the requirement is to design an architecture capable of generating discrete frequencies across four frequency bands (a total of 995 × 200 kHz channels) at duplex spacings of 45, 80, and 95 MHz while maintaining good frequency and ... [full story]

TDMA systems have always required close control of burst shaping—the rise and fall of the power envelope either side of the slot burst. In GPRS this process has to be implemented on multiple slots with significant variations in power from ... [full story]

The power levels and power masks are described in GSM 11.10-1. Compliance requires the first time slot be set to maximum power (PMAX) and the second time slot to minimum power, with all subsequent slots set to maximum. PMAX is ... [full story]

There are two particular issues with GPRS RF PA design:  The duty cycle can change from 1/8 to 8/8.  Power levels can change between time slots. The need to improve power efficiency focuses a substantial amount of R&D ... [full story]

One problem with the architectures considered so far is that the final frequency is generated at the start of the transmitter chain and then gained up through relatively (tens of MHz) wideband stages. The consequence of this is to cause ... [full story]

We identified in Chapter 1 a number of modulation techniques, including GMSK for GSM, π/4DQPSK for IS54 TDMA, 8 PSK for EDGE, and 16-level QAM for CDMA2000 1 × EV. To provide some design standardization, modulation is usually achieved through ... [full story]

Direct conversion receivers provide an elegant way of reducing component count, and component cost and increased use of baseband processing have meant that DCR can be applied to GPRS phones, including multiband, multimode GPRS. Careful impedance matching and attention to ... [full story]

In this section we consider an alternative architecture to the superhet�"the direct conversion receiver (DCR). Direct conversion receivers, also referred to as zero IF (ZIF), were first used in amateur radio in the 1950s, then HF receivers in the 1960s ... [full story]

The traditional receiver architecture of choice has been, and in many instances continues to be, the superheterodyne, or “superhet.” The principle of the superhet, invented by Edwin Armstrong early in the twentieth century, is to take the incoming received signal ... [full story]

We can now summarize the design objectives for a GSM multislot GPRS phone capable of working in several (three or four) frequency bands and capable of supporting other modulation techniques, such as non-constant envelope, and multiplexing (TDMA or CDMA) options. ... [full story]

In addition to supporting multiple frequency bands, there is a perceived—and actual—market need to accommodate multiple modulation and multiplexing techniques. In other words, the designer needs to ensure a handset is capable of modulating and demodulating GSM GMSK (a two-level ... [full story]

In Chapter 1 we described frequency allocations in the 800, 900, 1800, and 1900 MHz bands. For a handset to work transparently in Europe, the United States, and Asia, it is necessary to cover all bands (800 and 1900 MHz ... [full story]

The idea of a multislot phone is that we can give a user more than one channel. For instance, one slot could be supporting a voice channel, other slots could be supporting separate but simultaneous data channels, and we can ... [full story]

In this chapter we examine the hardware requirements for a GPRS tri-band phone capable of supporting higher-level modulation techniques. We address the design issues introduced by the need to produce the following: A multislot handset. Capable of supporting GSM (8 ... [full story]

Bandwidth quality in a radio system is normally measured in terms of bit error rate. It can also be measured in terms of frame erasure rate—the number of frames so severely errored they have to be discarded. We have said ... [full story]

We also mentioned in passing the Rayleigh fading experienced on the radio channel and the mechanisms we need to adopt to average out these channel impairments. These include interleaving, frequency hopping (a GSM handset must be capable of hopping every ... [full story]

Convolution and Correlation Convolutional encoding is a key mechanism for delivering coding gain, or sensitivity, in 2G and 3G cellular handsets. A further development of convolutional encoding, called turbo coding, is proposed for 3G handsets. Here two or more ... [full story]