TD 傳輸信道物理信道映射.ppt

1、Services provided by the physical layer,For TD-SCDMA (R4) Created by Fanjianfa,Interfaces to the physical layer,The physical layer (layer 1) is the lowest layer in the OSI Reference Model and it supports all functions required for the transmission of bit streams on the physical medium. The physical

2、layer interfaces the Medium Access Control (MAC) Layer and the Radio Resource Control (RRC) Layer as depicted in figure :,MAC,The physical layer interfaces the MAC entity of layer 2. Communication between the Physical Layer and MAC is in an abstract way performed by means of PHYprimitives defined wh

3、ich do not constrain implementations. The PHYprimitives exchanged between the physical layer and the data link layer provide the following functions: -transfer of transport blocks over the radio interface; -indicate the status of the layer 1 to layer2.,Formats and configurations for L1 data transfer

4、,Layer 2 is responsible for the mapping of data onto L1 via the L1/L2 interface that is formed by the transport channels. In order to describe how the mapping is performed and how it is controlled, some definitions and terms are required. The required definitions are given in the following subclause

5、s. Note that the definitions are generic for all transport channel types, i.e. not only for DCHs. All Transport Channels are defined as unidirectional (i.e. uplink, downlink, or relay-link). This means that a UE can have simultaneously (depending on the services and the state of the UE) one or sever

6、al transport channels in the downlink, and one or more Transport Channel in the uplink.,Transport Block,Transport Block: This is the basic unit exchanged between L1 and MAC, for L1 processing. Layer 1 adds a CRC for each Transport Block. Transport Block Set :This is defined as a set of Transport Blo

7、cks, which are exchanged between L1 and MAC at the same time instance using the same transport channel. Transport Block Size :This is defined as the number of bits in a Transport Block. The Transport Block Size is always fixed within a given Transport Block Set, i.e. all Transport Blocks within a Tr

8、ansport Block Set are equally sized. Transport Block Set Size :This is defined as the number of bits in a Transport Block Set. Transmission Time Interval :This is defined as the inter-arrival time of Transport Block Sets, and is equal to the periodicity at which a Transport Block Set is transferred

9、by the physical layer on the radio interface.,Transport Block,Transport Format,This is defined as a format offered by L1 to MAC for the delivery of a Transport Block Set during a Transmission Time Interval on a Transport Channel. The Transport Format constitutes of two parts one dynamic part and one

10、 semi-static part. Attributes of the dynamic part are: -Transport Block Size; -Transport Block Set Size; -Transmission Time Interval . Attributes of the semi-static part are: -Transmission Time Interval ; -error protection scheme to apply: -type of error protection; -coding rate; -static rate matchi

11、ng parameter; -size of CRC.,Transport Format Set,This is defined as the set of Transport Formats associated to a Transport Channel. The semi-static parts of all Transport Formats are the same within a Transport Format Set. Effectively the first two attributes of the dynamic part form the instantaneo

12、us bit rate on the Transport Channel. Variable bit rate on a Transport Channel may, depending on the type of service, which is mapped onto the transport channel,Transport Format Combination,The layer 1 multiplexes one or several Transport Channels, and for each Transport Channel, there exists a list

13、 of transport formats (Transport Format Set) which are applicable. Nevertheless, at a given point of time, not all combinations may be submitted to layer 1 but only a subset, the Transport Format Combination. This is defined as an authorised combination of the combination of currently valid Transpor

14、t Formats that can be submitted simultaneously to the layer 1 for transmission on a Coded Composite Transport Channel of a UE, i.e. containing one Transport Format from each Transport Channel. Transport Format Combination Set defined as a set of Transport Format Combinations on a Coded Composite Tra

15、nsport Channel.,Transport Format Indicator,The TFI is a label for a specific transport format within a transport format set. It is used in the inter-layer communication between MAC and L1 each time a transport block set is exchanged between the two layers on a transport channel. When the DSCH is ass

16、ociated with a DCH, the TFI of the DSCH also indicates the physical channel (i.e. the channelisation code) of the DSCH that has to be listened to by the UE.,Transport Format Combination Indicator,This is a representation of the current Transport Format Combination. There is a one-to-one corresponden

17、ce between a certain value of the TFCI and a certain Transport Format Combination. The TFCI is used in order to inform the receiving side of the currently valid Transport Format Combination, and hence how to decode, de-multiplex and deliver the received data on the appropriate Transport Channels. MA

18、C indicates the TFI to Layer 1 at each delivery of Transport Block Sets on each Transport Channel. Layer 1 then builds the TFCI from the TFIs of all parallel transport channels of the UE , processes the Transport Blocks appropriately and appends the TFCI to the physical control signalling. Through t

19、he detection of the TFCI the receiving side is able to identify the Transport Format Combination. For FDD, in case of limited Transport Format Combination Sets the TFCI signalling may be omitted, instead relying on blind detection. Nevertheless, from the assigned Transport Format Combinations, the r

20、eceiving side has all information it needs in order to decode the information and transfer it to MAC on the appropriate Transport Channels.,EXAMPLE,Physical channels and mapping of transport channelsonto physical channels,For TD-SCDMA (R4) Created by Fanjianfa,Transport channels,Transport channels a

21、re the services offered by layer 1 to the higher layers. A transport channel is defined by how and with what characteristics data is transferred over the air interface. A general classification of transport channels is into two groups:-Dedicated Channels, using inherent addressing of UE -Common Chan

22、nels, using explicit addressing of UE if addressing is needed,Dedicated transport channels,The Dedicated Channel (DCH) is an up- or downlink transport channel that is used to carry user or control information between the UTRAN and a UE.,Common transport channels,There are six types of transport chan

23、nels: - BCH- FACH- PCH - RACH- USCH- DSCH,BCH - Broadcast Channel,The Broadcast Channel (BCH) is a downlink transportchannel that is used to broadcast system- and cell-specific information.,FACH Forward Access Channel,The Forward Access Channel (FACH) is a downlink transport channel that is used to

24、carry control information to a mobile station when the system knows the location cell of the mobile station. The FACH may also carry short user packets,PCH Paging Channel,The Paging Channel (PCH) is a downlink transport channel that is used to carry control information to a mobile station when the s

25、ystem does not know the location cell of the mobile station.,RACH Random Access Channel,The Random Access Channel (RACH) is an up link transport channel that is used to carry control information from mobile station. The RACH may also carry short userpackets.,USCH Uplink Shared Channel,The uplink sha

26、red channel (USCH) is an uplink transport channel shared by several UEs carrying dedicated control or traffic data,DSCH Downlink Shared Channel,The downlink shared channel (DSCH) is a downlink transport channel shared by several UEs carrying dedicated control or traffic data.,Physical channels,All p

27、hysical channels take three-layer structure with respect to timeslots, radio frames and system frame numbering (SFN). Depending on the resource allocation, the configuration of radio frames or timeslots becomes different. All physical channels need guard symbols in every timeslot. The time slots are

28、 used in the sense of a TDMA component to separate different user signals in the time and the code domain.,Physical channels,A physical channel in TDD is a burst, which is transmitted in a particular timeslot within allocated Radio Frames. The allocation can be continuous, i.e. the time slot in ever

29、y frame is allocated to the physical channel or discontinuous, i.e. the time slot in a subset of all frames is allocated only. A burst is the combination of a data part, a midamble and a guard period. The duration of a burst is one time slot. Several bursts can be transmitted at the same time from o

30、ne transmitter. In this case, the data part must use different OVSF channelisation codes, but the same scrambling code. The midamble part has to use the same basic midamble code, but can use different midambles.,Physical channel signal format,Structure of the sub-frame,asymmetric DL/UL allocation,bu

31、rst structure of the DwPCH,burst structure of the UpPCH,GP,GP,Spreading,Spreading is applied to the data part of the physical channels and consists of two operations. The first is the channelisation operation, which transforms every data symbol into a number of chips, thus increasing the bandwidth o

32、f the signal. The number of chips per data symbol is called the Spreading Factor (SF). The second operation is the scrambling operation, where a scrambling code is applied to the spread signal.,Burst Format,A traffic burst consists of two data symbol fields, a midamble of 144 chips and a guard perio

33、d. The data fields of the burst are 352 chips long. The corresponding number of symbols depends on the spreading factor, as indicated in table 9 below. The guard period is 16 chip periods long.,Burst Format,Burst structure of the traffic burst format,traffic burst format,number of symbols per data f

34、ield in a traffic burst,number of symbols per data field in a traffic burst,Midamble,Transmission of TFCI,The traffic burst format provides the possibility for transmission of TFCI in uplink and downlink. The transmission of TFCI is negotiated at call setup and can be re-negotiated during the call.

35、For each CCTrCH it is indicated by higher layer signalling, which TFCI format is applied. Additionally for each allocated timeslot it is signalled individually whether that timeslot carries the TFCI or not. If a time slot contains the TFCI, then it is always transmitted using the first allocated cha

36、nnelisation code in the timeslot, according to the order in the higher layer allocation message.,Transmission of TFCI,Transmission of TFCI,Transmission of SS,The SS command is spread with the same spreading factor (SF) and spreading code as the data parts of the respective physical channel. The SS i

37、s utilised to command a timing adjustment by (k/8) Tc each M sub-frames, where Tc is the chip period. The default k and M values are signalled by the network by means of system information that is broadcast in the cell. The SS, as one of L1 signals, is to be transmitted once per 5ms sub-frame. M (1-

38、8) and k (1-8) can be adjusted during call setup or readjusted during the call,SS Position,Transmission of TPC,For every user the TPC information is to be transmitted at least once per 5ms sub-frame. If applied, transmission of TPC is done in the data parts of the traffic burst and it can be transmi

39、tted using the first allocated channelisation code and the first allocated timeslot (according to the order in the higher layer allocation message). Other allocations (more than one TPC transmission in one sub-frame) of TPC are also possible. The TPC is spread with the same spreading factor (SF) and

40、 spreading code as the data parts of the respective physical channel.,TPC Position,Transmission of TPC,For the number of layer 1 symbols per channelisation code there are 3 possibilities for each channelisation code, configured by higher layers: 1)one SS and one TPC symbol 2)no SS and no TPC symbols

41、 3)16/SF SS and 16/SF TPC symbols So, in case 3), when SF=1, there are 16 TPC symbols which correspond to 32 bits (for QPSK)。,DPCH,The DCH is mapped onto the dedicated physical channel（DPCH） . Spreading is applied to the data part of the physical channels and consists of two operations. The first is

42、 the channelisation operation, which transforms every data symbol into a number of chips, thus increasing the bandwidth of the signal. The number of chips per data symbol is called the Spreading Factor (SF). The second operation is the scrambling operation, where a scrambling code is applied to the

43、spread signal.,Common physical channels P-CCPCH,The BCH is mapped onto the Primary Common Control Physical Channels (P-CCPCH1 and P-CCPCH2). The position (time slot / code) of the P-CCPCHs is fixed in the 1.28Mcps TDD. The P-CCPCHs are mapped onto the first two code channels of timeslot#0 with sprea

44、ding factor of 16. The P-CCPCH is always transmitted with an antenna pattern configuration that provides whole cell coverage.,Common physical channels S-CCPCH,PCH and FACH are mapped onto one or more secondary common control physical channels (S-CCPCH). In this way the capacity of PCH and FACH can b

45、e adapted to the different requirements. The time slot and codes used for the S-CCPCH are broadcast on the BCH. The S-CCPCH uses fixed spreading with a spreading factor SF = 16. The S-CCPCHs ( S-CCPCH 1 and S-CCPCH 2 ) are always used in pairs, mapped onto two code channels with spreading factor 16.

46、 There can be more than one pair of S-CCPCHs in use in one cell.,Common physical channels F-PACH,The Fast Physical Access Channel (FPACH) is used by the Node B to carry, in a single burst, the acknowledgement of a detected signature with timing and power level adjustment indication to a user equipme

47、nt. FPACH makes use of one resource unit only at spreading factor 16, so that its burst is composed by 44 symbols. The spreading code, training sequence and time slot position are configured by the network and signalled on the BCH.,Common physical channels PRACH,The RACH is mapped onto one or more u

48、plink physical random access channels (PRACH). In such a way the capacity of RACH can be flexibly scaled depending on the operators need. The uplink PRACH uses either spreading factor SF=16, SF=8 or SF=4. The set of admissible spreading codes for use on the PRACH and the associated spreading factors

49、 are broadcast on the BCH (within the RACH configuration parameters on the BCH).,Common physical channels PICH,The Paging Indicator Channel (PICH) is a physical channel used to carry the paging indicators. the structure of a PICH transmission and the numbering of the bits within the bursts. The burs

50、t type is used for the PICH. NPIB bits are used to carry the paging indicators.,paging indicator carrying bits in the PICH bursts,Mapping of transport channels to physical channels,Multiplexing and channel coding (TDD),Multiplexing/channel coding/interleaving,Data stream from/to MAC and higher layer

51、s (Transport block / Transport block set) is encoded/decoded to offer transport services over the radio transmission link. Channel coding scheme is a combination of error detection, error correcting (including rate matching), and interleaving and transport channels mapping onto/splitting from physic

52、al channels. In the UTRA-TDD mode, the total number of basic physical channels (a certain time slot one spreading code on a certain carrier frequency) per frame is given by the maximum number of time slots which is 15 and the maximum number of CDMA codes per time slot.,Multiplexing/channel coding/in

53、terleaving,Transport channel coding/multiplexing,Figure (show below) illustrates the overall concept of transport-channel coding and multiplexing. Data arrives to the coding/multiplexing unit in form of transport block sets, once every transmission time interval. The transmission time interval is tr

54、ansport-channel specific from the set 10 ms, 20 ms, 40 ms, 80 ms.,CRC attachment,Error detection is provided on transport blocks through a Cyclic Redundancy Check (CRC). The size of the CRC is 24, 16, 12, 8 or 0 bits and it is signalled from higher layers what CRC size that should be used for each t

55、ransport channel.,CRC attachment,Transport block concatenation /code block segmentation,All transport blocks in a TTI are serially concatenated. If the number of bits in a TTI is larger than the maximum size of a code block, then code block segmentation is performed after the concatenation of the tr

56、ansport blocks. The maximum size of the code blocks depends on whether convolutional, turbo coding or no coding is used for the TrCH.,Channel coding,channel coding schemes can be applied to transport channels: -convolutional coding; -turbo coding; no coding. Usage of coding scheme and coding rate fo

57、r the different types of TrCH is shown in tables 1 and 2. The values of Yi in connection with each coding scheme: -convolutional coding with rate 1/2: Yi = 2*Ki + 16; rate 1/3: Yi = 3*Ki + 24; -turbo coding with rate 1/3: Yi = 3*Ki + 12; -no coding: Yi = Ki.,Usage of channel coding scheme,Radio frame size equalisation,Radio frame size equalisation is padding the input bit sequence in order to ensure that the output can be segmented in data segments of same size,1st interleaving,The 1st interleaving is a block interleaver with inter-column permutations.,1st interleaving,Rat