5. RESULTADOS
5.1. Cuido Directo durante el período reproductivo:
I. Radio Chnnels
1) Types of packet data logical channels
Packet data logical channels can be divided into four types. They are packet data traffic channel (PDTCH), packet broadcast control channel (PBCCH), packet common control channel (PCCCH), and packet dedicated control channel (PDCCH). The following details the four types of channels respectively.
a) PDTCH
The PDCH is used to transmit the subscriber data under packet transfer mode and the transfer rate ranges from 0 to 22.8 kbit/s. All the PDCCHs are unidirectional. The PDTCH uplink (PDTCH/U) helps the MS to transmit the data to the GPRS network. The PDTCH downlink (PDTCH/D) helps the GPRS network to transmit the data to the MS. b) PBCCH
The PBCCH broadcasts the parameters needed by the MS to access the network for packet service. In addition, it also broadcasts the parameters used for circuit switched service. The GPRS-attached MSs monitor the PBCCH only.
If a cell has the PBCCH, corresponding prompt is present in the BCCH. That is, the MS will be told that this cell is configured with the PBCCH through SI13. If there is no PBCCH is the cell, the BCCH will broadcast the parameters used for packet service. c) PCCCH
The PCCH can be divided into the following types:
z Packet paging channel (PPCH)
It is applied to the downlink only and used to page the MS.
z Packet random access channel (PRACH)
It is applied to the uplink only and used to request one or more PDTCH for the MS.
z Packet access grant channel (PAGCH)
It is applied to the downlink only and used to allocate one or more PDTCH.
z Packet notification channel (PNCH)
It is applied to the downlink only and used to notify the MS that the PTM-M call exists. If there is no PCCCH in a cell, the information of the packet service is transmitted on the CCCH. If there is PCCCH, the information of the packet service is transmitted on the
2/27/2009 All rights reserved Page35 of 94 PCCCH, and the information of the circuit switched service can also be transmitted on the PCCCH.
d) PDCCH
The PDCCH can be divided into the following types:
z Packet associated control channel (PACCH)
It is bi-directional and used to transmit the packet signaling.
z Packet timing advance control channel uplink (PTCCH/U)
It is used to transmit the random access burst so that the BSS side can estimate the timing advance for the MS performing the packet service.
z Packet timing advance control channel downlink (PTCCH/D)
It is used to provide the information of timing advance for multiple MSs. A PTCCH/D matches multiple PTCH/Us.
2) Combination of the packet data logical channels There are the following combinations:
z PBCCH + PCCCH + PDTCH + PACCH + PTCCH z PCCCH + PDTCH + PACCH + PTCCH
z PDTCH + PACCH + PTCCH
If the cell needs the PBCCH, the first combination is used. A cell needs only one group of the combination only.
If a great number of MSs are present in a cell, one or more groups of the second combination can be configured when the PCCCH is busy. The second combination cannot be configured with a cell unless the first combination is configured.
The third combination is used to transmit the uplink and downlink packet data only. A cell can be configured with one or more groups of this combination.
3) Mapping transformation between logical channels and physical channels The GPRS channel adopts 52-multiframe structure. Each packet channel has 52 multiframes in total, four of which form a radio block. Therefore, a radio block consists of 12 radio blocks and 4 idle frames. Figure 10-7 shows the structure.
B0 B1 B2 X B3 B4 B5 X B6 B7 B8 X B9 B10 B11 X
B0-B11: 12 radio blocks X: idle frame
Figure 10-7 Structure of a radio channel
In a GPRS system, the packet logical channel has a mapping relationship with the PDCH physical channel according to the radio block sequence. That is, B0, B6, B3, B9, B1, B7, B4, B10, B2, B8, B5, B1.
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z For the PBCCH, it can be mapped to the B0, B3, B6, B9, and so on. The specific
numbe of radio blocks are decided by the parameter BS_PBCCH_BLKS according to how busy the PBCCH is.
z For the PCCCH, the PAGCH and the PPCH can be mapped to any radio block of
the downlink channels except the radio blocked seized by the PBCCH. The uplink radio blocks seized by the PRACH correspond to the radio blocks seized by the PBCCH, PAGCH, and PPCH.
z For the PDTCH, it can be mapped to all the radio blocks and is used to transmit the
packet data.
z For the PACCH, it can be mapped to all the radio blocks and is used to send the
control message.
z For the PTCCH, the 12th and the 38th uplink frames of each 52-multiframe form a
PPCCH/U channel, and the 12th and the 38th downlink frames of two neighboring 52-multiframe form a PTCCH/D channel.
II. Channel coding
A GPRS radio block can only bear 456 bits. Four coding schemes are available for the GPRS channel. They are CS-1, CS-2, CS-3, and CS-4.
When coding the channel according to CS-1, first add the USF to the data bit as information bit, and then add the block check sequence (BSC) to detect and correct the codes. After that, add the tail bits and convolute all the bits by half. Finally, the 456-bit channel code is obtained.
When coding the channel according to CS-2 and CS-3, first add the USF to the data bit as information bit, and then add the BCS to detect and correct the codes. After pre-coding the USF, add the tail bit and convolute all the bits by half using the chopping technologies. Finally, the 456-bit channel code is obtained.
When coding the channel according to CS-4, first add the USF to the data bit as information bit, and then add the BCS to detect and correct the codes. After that, pre-code the USF. Finally, the 456-bit channel code is obtained. Note that the CS-4 does not adopt convolutional codes.
For details, see Table 10-8.
Table 10-8 GPRS channel coding scheme Channel coding
scheme Data bit USF BCS Tail bit Data rate (kbit/s)
CS-1 181 3 40 4 9.05
CS-2 268 6 16 4 13.4
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CS-4 428 12 16 0 21.4
The data transmission rate and the requirement on transmission quality vary with the CS. The higher the data transmission rate, the higher the transmission quality is required. When transmitting the data, the BSS can adjust the channel CS according to the variation of the radio quality. In this case, the radio resource can be fully used and the data transmission rate can be enhanced based on the assurance of the transmission quality.
III. RLC/MAC block structure
When used for packet data transmission, the structure of the RLC/MAC block is different from that when it is used for control message transmsion.
1) RLC/MAC data block
The RLC/MAC data block consists of MAC header and RLC data block, the later of which consists of RLC header, RLC data unit, and reserved bit. And the RLC data unit contains the octets that are fragmented from one or more LLC PDU. Figure 10-8 shows the structure of the RLC/MAC data block
RLC/MAC block
RLC data unit
MAC header RLC header RLC data unit Reserved bit Figure 10-8 Structure of the RLC/MAC data block
The size of the RLC/MAC data block varies with the CS type. For details, see Table 10-9.
Table 10-9 The size of the RLC/MAC data block CS type The size of RLC/MAC data block when reserved bit is not
accounted (byte) Reserved bits
The size of RLC/MAC data block (byte)
CS1 22 0 22
CS2 32 7 32 7/8
CS3 38 3 38 3/8
CS4 52 7 52 7/8
2) RLC/MAC control block
The RLC/MAC block used for the control message transmission consists of MAC header and RLC/MAC control block. Figure 10-9 shows the structure of the RLC/MAC block.
RLC/MAC block
2/27/2009 All rights reserved Page38 of 94 Figure 10-9 Structure of RLC/MAC block
3) Field remark
The following provides the remarks on the main fields. a) USF field
The USF field is transmitted in all uplink RLC/MAC blocks. It indicates the owner of the downlink block or the user of the next radio block of the same timeslot. When performing dynamic allocation, the network side uses the USF to allocate the uplink radio resources to the MS. The USF field stands for the eight different values composed of the binary codes. On the PCCCH, the value of the USF is 111, indicating that the corresponding uplink block is the uplink random access block.
b) SI bit
The SI bit stands for suspend indication bit. In the window mechanism, the SI bit indicates whether the RLC transmit window of the MS needs the suspension. The MS must set the SI bit in all uplink RLC data blocks. For the meaning of the SI bit, see Table 10-10.
Table 10-10 Meaning of the SI bit
Value Meaning
0 The RLC transmit window of the MS does not need suspension. 1 The RLC transmit window of the MS needs suspension.
c) S/P bit
The S/P bit stands for the supplementary/polling bit. It is used to indicate whether the relative reserved block period (RRBP) field is valid or not. For the meaning of the S/P bit, see Table 10-11.
Table 10-11 Meaning of the S/P bit
Value Meaning
0 The RRBP field is invalid.
1 The RRBP field is valid.
2/27/2009 All rights reserved Page39 of 94 The RRBP stands for relative reserved block period. This field indicates the location of the uplink blocks where the network side sends the PACKET CONTROL ACK message or the PACKET DL ACK/NACK message to. The value of the RRBP bit ranges from 0 to 3. For the meaning of the RRBP field, see Table 10-12.
Table 10-12 Meaning of the RRBP field Value Meaning
00 TDMA frame number = (N+3) mod 2715648 uplink block
01 TDMA frame number = (N+17 or N+18) mod 2715648 uplink block 10 TDMA frame number = (N+21 or N+22) mod 2715648 uplink block 11 TDMA frame number = (N+26) mod 2715648 uplink block
e) Effective payload type
This field indicates the range of the effective data contained in the RLC/MAC block. For the meaning of this field, see Table 10-13.
Table 10-13 Meaning of the effective payload type Value Meaning
00 The RLC/MAC block contains one RLC data block.
01 The RLC/MAC block contains one RLC control block but not contains the optional bytes in the RLC/MAC control header.
10 On the downlink, the RCL/MAC block contains both one RLC control block and the first optional byte in the RLC/MAC control header. 11 Reserved.
f) FBI bit
The FBI bit stands for the final block indicator bit, indicating the final downlink RLC data block in the downlink TBF. For the meaning of the FBI bit, see Table 10-14.
Table 10-14 Meaning of the FBI bit
Value Meaning
0 The current block is not the final RLC data block in the TBF. 1 The current block is the final RLC data block in the TBF.
2/27/2009 All rights reserved Page40 of 94 g) RTI field
The RTI stands for the radio transaction identifier. This field is used to number a group of the RLC/MAC blocks constituting a RLC control message. A RTI consists of 5 bits, and its value ranges from 1 to 31.
h) TFI field
The TFI field stands for the temporary block flow identifier field. It identifies all the TBFs affiliated to the RLC. Different channels can share the same TFI, which can identify the same TBF and different TBFs. The TBI of a channel is affiliated to an uplink or downlink TBF only at any time. The same MS can use either the same TFI or different TBIs during TBF transmission. Both the uplink TFI and downlink TFI are 5-bit binary codes, and their value ranges from 0 to 31.
i) BSN field
The BSN field stands for the block sequence number field. It is the number of each of the RLC data blocks in the TBF. The BSN is the 7-bit binary code, and its value ranges from 0 to 127.
IV. MS multislot capability
The MS multislot capability is divided into 27 classes. The number of the packet channels can be used by the MS simultaneously varies with the multislot capability class. The MS reports its multisolt capability class in the packet resource request message. When allocating the radio resource to the MS, the BSS must consider multiple factors, such as the amount of the data to be transmitted, the required QoS, and the number of available radio channels. If the radio resource can be fully used, the multislot capability class of the MS should be ensured to the maximum.
Table 10-15 lists the multislot capability of the MS. Table 10-15 MS multislot capability
Multislot
capability class Maximum timeslots Multislot capability class Maximum timeslots
Rx Tx Sum Rx Tx Sum 1 1 1 2 16 6 6 NA 2 2 1 3 17 7 7 NA 3 2 2 3 18 8 8 NA 4 3 1 4 19 6 2 NA 5 2 2 4 20 6 3 NA 6 3 2 4 21 6 4 NA 7 3 3 4 22 6 4 NA 8 4 1 5 23 6 6 NA 9 3 2 5 24 8 2 NA 10 4 2 5 25 8 3 NA
2/27/2009 All rights reserved Page41 of 94 11 4 3 5 26 8 4 NA 12 4 4 5 27 8 4 NA 13 3 3 NA 28 8 6 NA 14 4 4 NA 29 8 8 NA 15 5 5 NA Note:
z Rx indicates the maximum timeslots used by the MS for downlink transmission in a TDMA frame.
z Tx indicates the maximum timeslots used by the MS for uplink transmission in a TDMA frame.
z Sum indicates the sum of the timeslots used by the MS for data transmission in a TDMA frame. That is, the number of the timeslots used by the MS for uplink and downlink transmission must be equal to or less than the value of the Sum.
According to the multislot capability class configured with the MS, the MS can be divided into two types. That is, type 1 and type 2. In the 29 multislot capability classes, the MSs whose multislot capability classes are 1-12 and 19-29 belong to type 1, and the MSs whose multislot capability classes are 13-18 belong to type 2. The MSs of type 1 cannot transmit and receive data simultaneously, while the MSs of type 2 can. V. DRX
The DRX stands for discontinuous reception. To reduce the power consumption in idle state, the MS needs to adopt the DRX model. Under this model, the MS receives the related paging messages on the paging channels only regardless of the paging type. When attaching to the GPRS, the MS needs to notify the GPRS/GSM network whether it supports the DRX or not. If yes, the MS works according to the DRX parameters received from the network. For the current network, it determines the paging group that the MS belongs to according to the BS_PA_MFRMS received on the CCCH.
VI. Power control
Currently, the GPRS system provides the algorithms for uplink open loop power control. The open power control is based on the assumption that the uplink and downlink have the same path loss. Therefore, the MS can adjust the output power according to the level of the received signals. The power control parameters are delivered in the SI13. In the GPRS system, the algorithm for uplink power control is expressed as follows: PCH = min (Γ0 - ΓCH - α * (C + 48), PMAX)
Here,
z PCH is the output power of the MS during uplink power control z Γ0 is the maximum transmit power of the MS
z ΓCH is the power control parameter sent by the network side to the MS. z α is the power control parameter sent by the network side to the MS
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z C is the normalized level of the received signals. It is the average level of the
bursts of 4 TDMA frames in a radio blocks.
z PMAX is the maximum transit power of the MS allowed by the cell, and it is
delivered in the system information.
For open loop power control, the α = 1.0, so PCH = min (Γ0 - ΓCH - C - 48), PMAX).
When the MS performs the uplink open loop power control, the values of Γ0, C, and
PMAX are known for the MS. The value of the ΓCH is calculated by the network side
according to the BTS receiving level, BTS transmit power, and the maximum MS transmit power. In addition, the value of the ΓCH can be sent to the MS in the RLC/MAC
control message.
When the MS performs the downlink open loop power control, it uses the same power to transmit the 4 TDMA frames in a radio block. When the MS has reselected and entered a new cell, it must transmit the data with the maximum output before receiving the power control parameters from the cell.
VII. Timing advance control
Because the packet data is discontinuously transmitted, it is hard for the network side to obtain the timing advance (TA) of the MS. As a result, the downlink data may not be normally received. Therefore, the GPRS system introduces a new timing advance algorithm, which is divided into initial timing advance control algorithm and continuous timing advance control algorithm. In this case, the valid TA can always be obtained. 1) Initial timing advance control algorithm
When the MS accesses the network, the BTS uses this algorithm to calculate the TA of the MS according to the access burst received on the PACH (the MS sends the access burst). After that, the BTS delivers the BTS to the MS in a Packet Assignment message. If a TBF is established during uplink or downlink data transmission, the Packet Downlink Assignment message may not include TA. In this case, the network side can set the polling bits in the Packet Downlink Assignment message. After receiving the message, the MS will send a Packet Control Ack/Nack message to the network side to help it to obtain the TA.
In addition, when the MS has sent a Packet Channel Request message, the network cannot necessary deliver a Packet Assignment message to the MS due to no available resource. In this case, to obtain the TA, the network side can enable the packet polling procedure to send a Packet Polling message to make the MS send 4 Packet Ack/Nack messages in the form of bursts.
If the Packet Assignment message does not include TA, the MS can obtain the TA from the Packet Power Control/Timing Advance message or the timing advance update only.
2/27/2009 All rights reserved Page43 of 94 2) Continuous timing advance control algorithm
This algorithm is applied to the packet transfer mode. The MS ascertains the PTCCH allocated to it the according to the TAI sent in the Packet Assignment message and sends the access bursts on the corresponding PTCCH. (The TAI stands for timing advance index, and its value ranges from 0 to 15.). The network side calculates the new TA of the MS according to the received access bursts. After that, it tells the TA to the MS through the corresponding PTCCH, or the Packet Power Control/Timing Advance message and the Packet Uplink ack/Nack message.