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Calculation of CPRI interface SFP
1. Basic information
The CPRI specification enables flexible and efficient product differentiation for radio base stations and independent technology evolution for Radio Equipment (RE) and Radio Equipment Control (REC).
1.1.
CPRI Line Bit Rate
In order to achieve the required flexibility fl exibility and cost efficiency, several different line bit rates are defined. • CPRI line bit rate option 1: 614.4 Mbit/s • CPRI line bit rate option 2: 1228.8 Mbit/s (2 x 614.4 Mbit/s) • CPRI line bit rate r ate option 3: 2457.6 Mbit/s (4 x 614.4 Mbit/s) • CPRI line bit rate option 4: 3072.0 Mbit/s (5 x 614.4 Mbit/s) • CPRI line bit rate option 5: 4915.2 Mbit/s (8 x 614.4 Mbit/s) • CPRI line bit rate option 6: 6144.0 Mbit/s (10 x 614.4 Mbit/s)
It is mandatory that each REC and RE support at least one of the above cited CPRI line bit rates. All CPRI line bit rates have been chosen in such a way that the basic UMTS chip rate of 3.84 M bit/s can be recovered in a cost-efficient way from the line bit rate taking into account the 8B/10B line coding.
1.2.CPRI Basic Frame The length of a basic frame is 1 TC = 1/fc = 1/3.84 MHz = 260.416667ns. A basic frame consists of 16 words with index W=0…15. The word with the index W=0, 1/ 16 of the basic frame, is used for one control word.
1.3.Antenna-Carrier(AxC): One antenna-carrier is the amount of digital baseband (IQ) U-plane data necessary for either reception or transmission of only one carrier at one independent antenna element. ZTE definition is 30 bits.
AxC Container: For E-UTRA it contains one or more IQ samples for the duration of one UMTS chip or it contains IQ sample bits and sometimes also stuffing bits. Chip Value = Length of word * Number of word AxC No./Chip= Chip Value / AxC value
2. Optical port resource
2.1.GSM In the GSM mode, the sample rate is 1.288 MSPS, it means 1.288M sample points per second need to be transferred. So each CPRI basic frame (1/3.84 MHz) need to pass 1/3 GSM sampling point. Since each sample point contain I and Q per 15bit, so each GSM TRX needs to occupy 1/3 AXC carrier container.
2.2.UMTS In the UMTS mode, the sample rate is 3.84 MSPS, it means 3.84M sample points per second need to be transferred. So each CPRI basic frame (1/3.84Mhz) need to pass a UMTS sampling point. Since each sample point contain I and Q per 15bit, so each UMTS Carrier needs to occupy 1 AXC carrier container.
2.3.LTE LTE baseband, Intermediate frequency IQ uses 15 bits, in order to reduce the rate of optical port, the optical port uses compression technology of 9bit. Using 9bit compressed, the IQ bit width is 9bit between BBU and RRU.
3.Quick guide CPRI bit rate and corresponding Axc
CPRI bit rate and corresponding BW , No. of antenna , normal sample rate BW
20
DL/UL
20
DL
UL
15 DL
15 UL
10 DL
10 UL
5 DL
5 UL
No.antenna
2
4
2
4
2
2
2
2
IQ value(bite)
9
9
9
9
9
9
9
9
normal sample rate
30.72
30.72
30.72
30.72
30.72
30.72
30.72
30.72
Low sample rate
23.04
23.04
23.04
23.04
23.04
23.04
23.04
23.04
IQ data bit rate(Mbps)
1474.56
2949.13
1474.56
2949.13
737.28
737.28
368.64
368.64
IQ data bit rate(Mbps)
1105.92
2211.85
1105.92
2211.85
737.28
737.28
368.64
368.64
CPRI line bit rate(Gbps)
3.072
3.072
3.072
3.072
1.2288
1.2288
0.6144
0.6144
CPRI line bit rate(Gpbs)
2.4576
2.4576
2.4576
2.4576
1.2288
1.2288
0.6144
0.6144
Axc and corresponding scenarios . It can be quickly to calculate the SFP with this table. AXC
1TR 20/15M
1TR 20/15M
2TR 10M
number
antenna(normal)
antenna(Low sample)
antenna
AXC(30bit)
5
4
UMTS 5
2
GSM(1T2R) 1/3
For example，LTE 20MHz + 8TRX = 8 + 3 = 11 AxC <16 , 2.5G Optical Module is enough
4.Conclusion 4.1.GSM MODE GSM Data Rate: 26 frames in 15ms Sample Rate: 156.25* 26 / 15 = 270.833KHz 4 Times interpolation: 270.833 *4 = 1.08333MHz So GSM take as 1.28MHz, it is 1/3 AxC
