TSG-RAN WG1 Meeting#44
`Denver, USA, February 13-17, 2006
`
`Source:
`Title:
`Agenda Item:
`Document for:
`
`
`Panasonic
`RACH preamble evaluation in E-UTRA uplink
`13.2.3.1
`Discussion
`
`R1-060700
`
`Introduction
`1.
`Random access channel (RACH) is used for the initial physical connection on initial cell access, handover and
`the resource allocation when the UE uplink has not been time synchronized. Several discussions on RACH to
`achieve short initial physical connection setup have also been reported in [4] - [7] . RACH sub-frame may be
`composed of a preamble part and a message part. We evaluate the preamble performance. Based on the
`evaluation results, we discuss the inclusion of message part on RACH.
`2. Discussion
`2.1. RACH requirements
`In RACH structure design, the following requirements have been considered [1] [3] - [10] .
` Reliable acquisition of preamble
` Estimation of arrival timing
` Reduction in the whole process delay
` To minimize RACH time-frequency resources regarding spectrum efficiency
`The most important requirement of the above is reliable acquisition and estimation of arrival timing because the
`success rate of RACH attempt should be high enough. The inclusion of message part on RACH has been
`considered to shorten physical connection setup delay [4] - [7] .
`
`
`2.2. Discussion on RACH preamble length
`In TR [2] , E-UTRA is required to support at least 30km cell size. Therefore, we showed the link budget and
`achievable number of bits per TTI (0.5ms) to estimate how many bits can be contained on RACH in [10] . The
`result would be useful in the case coverage is critical although the result is still preliminarily. On the other hand,
`we also need the discussion in the case that interference is critical. [6] reports that approximately -13 dB and -18
`dB of the average received Es/No were derived from the system level evaluation. As mentioned above, the most
`important RACH functions are reliable acquisition, and estimation of arrival timing. For these reasons, first, we
`evaluate the required RACH preamble length that corresponds to the required average received Es/No. Next we
`discuss the possibility of the inclusion of message part.
`In the RACH preamble evaluation, we assume the followings:
` RACH TTI is a multiple of 0.5msec. RACH preamble, guard time and possibly message part share a
`RACH TTI
` Random access channel is time/frequency multiplexed with other channels[3] [4]
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`-1/5-
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`ZTE/SAMSUNG 1002-0001
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`APPLE 1002
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`Preamble structure
`A preamble sequence should have a good auto-correlation and good-cross correlation. General chirp-like (GCL)
`has been considered to satisfy these requirements [5] [8] [9] . In our preamble performance evaluation, Zadoff-
`Chu CAZAC sequence [13] , a special case of GCL, is used. RACH preamble structure is shown in Figure 1.
`We evaluated 1.25MHz and 5MHz as transmission bandwidth of the RACH. The preamble structure consists of
`M-times repetition of N=73 (1.25MHz) or N=293(5MHz) CAZAC sequence. Cyclic prefix and guard time are
`also included within a RACH TTI.
`
`
`M Repetition (M=3(200u)/ 7(467us) /14 (933us) / 28(1867us))
`
`CP
`
`CAZAC sequence
`N=73(1.25MHz), N=293(5MHz)
`
`CAZAC sequence
`
`CAZAC sequence
`
`Guard
`time
`
`128 sample
`
`512 samples (66.67us)
`
`RACH TTI length = 0.5 / 1.0 / 2.0 ms
`Figure 1 – RACH preamble structure
`
`remaining sample
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`Performance of preamble
`The simulation parameters are shown in Table 1. As preamble performance evaluation criteria, we used false
`alarm and miss detection probability to the average received Es/No. The definition is as follows:
` False alarm (Pfa): the probability of a particular code being detected when nothing, or different code was
`transmitted
` Miss detection (Pmd): the probability of a particular code not being detected when the code was
`transmitted
`Although time domain preamble detection would also possible, in our evaluation, the RACH preamble detection
`is performed in frequency domain, which is similar to the detection algorithm described in [8] .
`1. Repeated CAZAC sequences of the received signal are combined in time domain.
`2. The combined CAZAC sequence is processed by FFT.
`3. A transmitted CAZAC code is detected by using coherent detection in frequency domain.
`4. A delay profile response is obtained after IDFT processing.
`
`
`5MHz
`
`Table 1 – Simulation parameters
`1.25MHz
`Transmission Bandwidth
`Localized FDMA
`Transmission scheme
`0.5 ms / 1.0ms / 2.0ms
`RACH TTI length
`CAZAC sequence (Zadoff-Chu CAZAC[13] )
`Signature pattern
`Length of CAZAC sequence (N) 73
`293
`3 (total preamble length: 200usec)
`7 (total preamble length: 467usec)
`14 (total preamble length: 933usec)
`28 (total preamble length: 1867usec)
`
`11
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` transmit antenna, 2 receive antenna (combined non-coherently)
`Coherent detection in frequency-domain
`Preamble detaction in time-domain (after IDFT)
`AWGN
`Typical Urban model, 120km/h
`
`
`
`Repetition factor (M) of
`CAZAC sequence
`Number of multiplexed users
`Antenna configuration
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`Detector
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`Channel model
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`ZTE/SAMSUNG 1002-0002
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`Figure 2 and Figure 3 illustrate the miss detection probability (Pmd) to the average received Es/No of 1.25MHz
`and 5MHz bandwidth to achieve the false alarm Pfa = 10-3 under AWGN channel and TU 120km/h, respectively.
`
`
`False alarm Pfa = 10-3
`
`Bandwidth: 5MHz
`Channel: AWGN
` 3 repetition (200us)
` 7 repetition (467us)
` 14 repetition (933us)
` 28 repetition (1867us)
`
`Bandwidth: 1.25MHz
`Channel: AWGN
` 3 repetition (200us)
` 7 repetition (467us)
` 14 repetition (933us)
` 28 repetition (1867us)
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`100
`
`10-1
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`10-2
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`10-3
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`Miss detection probability (Pmd)
`
`10-4
`-35
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`-5
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`-30
`-25
`-20
`-15
`-10
`Average received Es/No [dB]
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`Figure 2 Miss detection probability (Pmd) to the average received Es/No (AWGN)
`100
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`False alarm Pfa = 10-3
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`Bandwidth: 5MHz
`Channel: TU 120km/h
` 3 repetition (200us)
` 7 repetition (467us)
` 14 repetition (933us)
` 28 repetition (1867us)
`
`Bandwidth: 1.25MHz
`Channel: TU 120km/h
` 3 repetition (200us)
` 7 repetition (467us)
` 14 repetition (933us)
` 28 repetition (1867us)
`
`10-1
`
`10-2
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`10-3
`
`Miss detection probability (Pmd)
`
`10-4
`
`-25
`
`0
`
`-20
`-15
`-10
`-5
`Average received Es/No [dB]
`
`Figure 3 Miss detection probability (Pmd) to the average received Es/No (TU 120km/h)
`
`
`
`
`Target value of the false alarm is  10-3 and the target value of miss detection is  10-2 and 10-3 in WCDMA [11] .
`We think similar target also would be required in LTE. Therefore, if we use the same target values, from the
`above results, we can derive the required preamble length to the average received Es/No. The required preamble
`length in 1.25MHz bandwidth is illustrated in Figure 4 to the average received Es/No to achieve Pmd  10-3 and
`Pmd  10-2 with false alarm Pfa = 10-3. Figure 5 shows the case of 5MHz bandwidth.
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`-3/5-
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`Bandwidth: 1.25MHz
` Pmd=10-3 (AWGN)
` Pmd=10-2 (AWGN)
`
` Pmd=10-3 (TU120km/h)
` Pmd=10-2 (TU120km/h)
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`2
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`1
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`0.5
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`0.2
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`Required preamble length [ms]
`
`
`
`
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`0.1
`-25
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`2
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`-20
`-15
`-10
`-5
`Average received Es/No [dB]
`Figure 4 Preamble length to Es/No of false alarm probability = 10-3 (1.25MHz)
`Bandwidth: 5MHz
` Pmd=10-3 (AWGN)
` Pmd=10-2 (AWGN)
`
`0
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` Pmd=10-3 (TU120km/h)
` Pmd=10-2 (TU120km/h)
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`1
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`0.5
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`0.2
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`Required preamble length [ms]
`
`0.1
`-30
`
`-25
`-20
`-15
`-10
`Average received Es/No [dB]
`Figure 5 Preamble length to Es/No of false alarm probability = 10-3 (5MHz)
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`-5
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`According to [6] , approximately -13 dB and -18 dB of the average received Es/No were derived from the system
`level evaluation for the ISD 500m and 1732m, respectively, when using open-loop TPC and 5MHz transmission
`bandwidth. Table 2 shows preamble length required for -13dB and -18dB of Es/No under AWGN and
`TU120km/h.
`Table 2 Required preamble length to the average received Es/No (5MHz bandwidth)
`Average received Es/No
`AWGN
`TU-120 km/h
`Pmd = 10-2
`Pmd = 10-3
`5-repetition
`7-repetition
`(333 usec)
`(467 usec)
`15-repetition
`28-repetition
`(1000 usec)
`(1867 usec)
`
`-13 dB (ISD=500m)
`
`-18 dB (ISD=1732m)
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`
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`Pmd = 10-2
`1-repetition
`(67 usec)
`3-repetition
`(200 usec)
`
`Pmd = 10-3
`2-repetition
`(133 usec)
`4-repetition
`(267 usec)
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`ZTE/SAMSUNG 1002-0004
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`In this evaluation, only one preamble is transmitted. If multiple preambles are transmitted and multiple
`preambles are also received at the same time, additional preamble length would be required due to multiple
`access interference (MAI).
`The available time-frequency resource to the message part could be following:
`Message part length [ms]
`
` = RACH TTI length [N x 0.5ms] – Preamble length [ms] – Guard time/Cyclic prefix [ms]
`
`
`
` A
`
` larger message part requires a larger RACH TTI. Nevertheless, the time and frequency resources allocated to
`RACH should be as small as possible because the spectrum efficiency of RACH would be much lower than that
`of scheduled channel.
`As a result, our current view is it would be difficult to include a large massage part in RACH TTI length from
`preamble performance perspective. The link budget calculation leads the same conclusion [10] . A small size of
`message part may be included depending on target Es/No.
`
`3. Conclusion
`In this contribution, we evaluated the preamble performance. Based on the evaluation results, we discussed the
`inclusion of message part on RACH. Our current view is that it would be difficult to include a large massage part
`in RACH due to the limitations imposed by the link budget and preamble performance. A small size of message
`part may be included depending on target Es/No.
`
`References
`[1] TR 25.814 V1.0.2, “Physical layer aspects for evolved UTRA”
`[2] TR25.913 V2.0.0, “Requirements for Evolved UTRA and UTRAN”
`[3] R1-051445, Ericsson, “E-UTRA Random Access”
`[4] R1-051391, NTT DoCoMo, “Random Access Transmission for Scalable Multiple Bandwidths in Evolved
`UTRA Uplink”
`[5] R1-060025, Motorola, “RACH Design for EUTRA”
`[6] R1-060047, NTT DoCoMo, NEC, Sharp, “Random Access Transmission in E-UTRA Uplink”
`[7] R1-060181, Qualcomm, “Characteristics of UL Access Channel”
`[8] R1-060152, Nortel, “Consideration on UL RACH scheme for LTE”
`[9] R1-060226, Huawei, “EUTRA RACH preambles”
`[10] R1-060161, Panasonic, “Inclusion of additional data on RACH”
`[11] R1-060061, “LTE L1 related questions to RAN1”
`[12] TR25.104 V6.11.0, “Base Station (BS) radio transmission and reception (FDD) (Release 6)”
`[13] D. C. Chu, “Ployphase codes with good periodic correlation properties,” IEEE Trans. Information Theory,
`vol.18, pp531-532, July 1972.
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