8 CLASIFICACIÓN
8.4 Métodos de evaluación de la clasificación
As with IMT2000DS, CDMA2000 is tightly specified in terms of spurious emissions, measured both for their impact in-band and out-of-channel, as shown in Figure 3.29.
In markets with legacy 30 kHz channel-spaced networks (US TDMA 800 MHz and 1900 MHz), adjacent channel power ratios need to be qualified with respect to adjacent narrowband channels. Similar specifications are required for out-of-band perfor- mance. The CDMA2000 specification requires spurious emissions outside the allocated system band (measured in a 30 kHz bandwidth) to be 60 dB below the mean output power in the channel bandwidth or -13 dBm, whichever is smaller.
Frame erasure rate can be used as a measure of receiver performance, provided cod- ing and error correction is applied equally to all bits—that is, there are not classes of bits with different levels of error correction. Frame erasure rate is the ratio of the num- ber of frames of data received that are deleted because of an unacceptable number of errors to the total number of frames transmitted. Frame erasure rate is used as a mea- sure of receiver performance.
Figure 3.29 In-band/out-of-channel measurements.
We can use frame erasure rate to measure sensitivity and dynamic range, spurious immunity, and performance in AWGN and fading channels. CDMA2000 uses 20 ms frames. Base station receiver performance is expressed in terms of FER versus Eb/No. The Eb/Norequired will be a function of data rate and channel requirements.
At system level, the use of a continuous pilot in CDMA2000 provides better channel sounding, compared to IMT2000DS, but it uses more transmit energy. The continuous common pilot channel provides the following:
■■ More accurate estimation of the fading channel
■■ Faster detection of weak multipath rays than the per-user pilot approach ■■ Less overhead per user
Turbo coding is used for higher data rates with K = 9 constraint length.
The forward link coding is adaptive. Interleaving can either be 20 or 5 ms. A 6-bit, 8- bit, 10-bit, 12-bit, or 16-bit CRC is used for frame error checking with 1/2, 1/3, 1/4 rate K=9 convolutional coding. Equivalent rate turbo codes are used on supplemental
1.98 MHz 750 kHz
-45 dBc
-60 dBc
channels. Each supplemental channel may use a different encoding scheme. Similarly, downlink coding is adaptive, using a 6-bit, 8-bit, 10-bit, 12-bit, or 16-bit CRC for frame error checking, and 9/16, 1/2, 1/3, 1/4 rate K = 9 convolutional coding. Equivalent rate turbo codes are used on supplemental channels. Each supplemental channel may use a different encoding scheme. Interleaving is again either 5 ms or 20 ms.
Closed-loop power control is carried out at an 800 Hz control rate. The open loop sets Tx power level based on the Rx power received by the mobile and compensates for path loss and slow fading. The closed loop is for medium to fast fading and provides com- pensation for open-loop power control inaccuracies. The outer loop is implementation- specific and adjusts the closed-loop control threshold in the base station to maintain the desired frame error rate. The step size is adaptive, either 1 dB, 0.5 dB, or 0.25 dB. As with IMT2000DS, power control errors will directly subtract from the link budget.
The power control dynamic range is as follows: ■■ Open loop ±40 dB
■■ Closed loop ±24 dB
Power control errors are typically 1.3 dB (low mobility) or 2.7 dB (high mobility). Dynamic range is similar to other existing networks:
Mobile 79 dB
Base station 52 dB
FDD isolation (45 MHz, 800 MHz, 80 MHz at 1900 MHz) Class II mobile 55 dB Tx to Rx
Base 90 dB (higher effective power, 5 dB lower noise floor) Class IV handsets are equivalent to Power Class 3 handsets in IMT2000DS (250 mW). Class V handsets are equivalent to Power Class 4 handsets in IMT2000DS (125 mW). Both networks also support higher-power mobiles.
Class I: 28 dBm < EIRP < 33 dBm (2 W)
Class II: 23 dBm < EIRP < 30 dBm
Class III: 18 dBm < EIRP < 27 dBm
Class IV: 13 dBm < EIRP < 24 dBm (250 mW)
Class V: 8 dBm < EIRP <21 dBm (125 mW)
CDMA 1xEV has a high data rate option for the downlink, separate 1.25 MHz RF channel, QPSK, 8 PSK, 16-level QAM, and evolution to meet IMT2000MC require- ments (3xRTT). 1xEV adds adaptive modulation as a mechanism for increasing data throughput.
Figure 3.30 CDMA2000 handset in a soft handoff.
The Media Access Control (MAC) layer in IS2000 manages code allocation (the pro- vision of physical layer resources to meet application layer requirements). An active high-rate mobile assigned a fundamental channel on origination negotiates high data rate service parameters. The mobile then sleeps but remains locked to a low-rate chan- nel for synchronization and power control.
The handset signals a high data burst request by indicating to the base station (BS) its data backlog and maximum data rate requested. The handset includes pilot strength information for cells in its neighbor list, which indicates local interference lev- els. Additionally pilot strength measurements allow the base station to qualify instan- taneous downlink capacity.
RLP IWF PDN MSC BS 1 BS 2 MS Fundamental Supplemental 1 Supplemental 2 Supplemental 3 Supplemental 4 Fundamental Supplemental 1 Supplemental 2 Supplemental 3 Supplemental 4
Supplemental code channels can then be allocated as required. In Figure 3.30, the handset communicates on the fundamental code channel with two base stations (BS1 and BS2). During a burst transmission, one or more supplemental code channels are assigned at BS1, BS2, or both. The MSC performs distribution on the forward link and selection on the reverse link. The Radio Link Protocol (RLP) does an Automatic Repeat Request (ARQ) and the interworking function (IWF) provides access to the packet data network.
When there is backlogged data, the mobile goes into active mode. If backlogged data exceeds a threshold, the mobile requests a supplementary channel (SCRM), sent on the fundamental code channel. The BS/MSC uses pilot strength measurements made by the mobile to decide on burst admission control and allocates supplementary channels. When backlogged data at the IWF exceeds a predetermined threshold, the IWF initi- ates a request for supplementary channels. The mobile is paged if not already in an active state.
In IS95B, a mobile is either active or dormant, and in CDMA2000, a handset can go into control hold, maintaining a dedicated control channel and power control (burst transmission with no added latency). In suspended state, there are no dedicated chan- nels, although a virtual set of channels are maintained. In dormant state, there are no pre-allocated resources; in other words, the deeper the sleep, the lower the power con- sumption, but the longer it takes to wake up.
Summary
In this chapter we summarized the main tasks that need to be performed by a 3G hand- set, and we qualified code domain, frequency domain, and time domain performance issues. Typically, over a 15-year maturation cycle, handset performances improves on a year-by-year basis. and this delivers benefits in terms of network bandwidth quality. In the following two chapters, we consider 3G handset hardware form factor and functionality and handset hardware evolution.
111 In Chapter 2 we described the physical hardware needed to realize a multislot, multi- band, multimode handset. In Chapter 3 we described the physical hardware needed to deliver multiple per-user channel streams. In this chapter we describe the application hardware components needed to realize a multimedia mobile handset and the impact of various hardware items in the handset on the offered traffic mix.