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UMTS Air Interface Overview

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Präsentation zum Thema: "UMTS Air Interface Overview"—  Präsentation transkript:

1 UMTS Air Interface Overview
Albrecht Kunz Hochschule für Technik und Wirtschaft des Saarlandes Saarbrücken, 04. Juli 2005

2 All-IP Based Multimedia Terminals The Ultimate Goal
If I would have had a mobile multimedia terminal, I could: - look an the e-map where I am - send an for some help - call my wife and kids and send them a picture of this beautiful location - get the latest news from the stockmarket while waiting. It would be great However I don‘t have a tool like that and I‘m lost. I‘m in trouble

3 Keller 22.976 Support of push service

4 3GPP Technical Specification Groups
Keller 3GPP Technical Specification Groups 22.976 Support of push service

5 Overview Motivation UMTS key characteristics CDMA Basics
Multipath reception / Rake receiver TX/RX baseband processing Transport & physical channels Frame structure Handover Power control

6 UMTS Key Characteristics

7 Quality of Service (QoS) - End to End delay
«Hi ! How are you ?» «Hi ! How... T small delays (10-20 ms) are not annoying for users delay < 200 to 400 ms, the effectiveness of the interaction is lower but can be still acceptable delay is > 400 ms, interactive voice communication is quite difficult

8 UMTS Terrestrial Radio Access (UTRA)
TDD mode FDD mode Time Division Duplex based on Delta Concept (TD-CDMA) Frequency Division Duplex based on Alpha Concept (DS-CDMA)

9 Air Interface Characteristics
time time Energy, Code Energy, Code Frequency Frequency TDD mode FDD mode

10 UMTS frequency bands 1900 1950 2000 2050 2100 2150 2200 1 2 4 1 2' 4 [MHz] 1 UMTS TDD (1900MHz-1920MHz,2010MHz-2025MHz) 2 UMTS uplink (FDD) (1920MHz-1980MHz) 2' UMTS downlink (FDD) (2110MHz-2170MHz) 4 UMTS Satellite (1980MHz-2010MHz, 2170MHz-2010MHz)

11 Frequency reuse R=1 R=3 R=4 R=7

12 Multiple Access FDMA TDMA CDMA P t f P t f P t f

13 Despreading P t f P t f

14 Multipath Propagation Environment
Channel Impulse response h(t,)

15 Channel model

16 Rake receiver

17 UMTS – Prinzip der Bandspreiztechnik Verwendung orthogonaler Spreizcodes, um die Nutzer in der Zelle zu separieren

18 Verwendung orthogonaler Spreizcodes: Spreizvorgang
Verwendete Modulationsart ist QPSK (downlink, d.h. Kommunikation von der Basisstation zur Mobilstation Codes unterschiedlicher Spreizfaktoren (Spreading Factor, SF) können verwendet werden Die okkupierte Bandbreite ist nach dem Spreizen SF-mal so groß Die spektrale Leistungsdichte wird durch den Spreizvorgang auf 1/SF reduziert

19 Entspreizvorgang: Entspreizen durch Multiplikation mit der gleichen Spreizfunktion, mit der gesendet wurde Anwendung eines Korrelators oder Matched Filters: Korrelator: Integration von SF Chips, bei Verwendung des richtigen Codes (phasensynchron zum Sender) tritt Korrelationsspitze auf Matched filter mit Entspreizsequenz (-t): Korrelationsspitze tritt auf bei vollständiger Überlappung von gesendeter Spreizsequenz und multiplizierter Entspreizsequenz Gleichheit der Sequenzen => +1*+1=1 und –1*-1=1 maximales Integrationsergebnis (Korrelationsspitze) ! Unterschiedliche Codes führen zu Nebenzipfeln, da die Codes nicht vollständig orthogonal sind (Bsp: siehe Gold-Codes)

20 Maximal LFSR Sequences = M-Sequences
There are LFSRs with L memory elements and characteristic polynomial Q(x) that produce sequences with maximum period of length 2L-1. The sequences are called maximal LFSR sequences or m-sequences. The characteristic polynomials are called primitive polynomials. Tables of primitive polynomials exist (e.g. in Peterson/Weldon,Error Correcting Codes,1972). Example: Degree 8 Q(x): 561 octal

21 Correlation Properties of M-Sequences
The out of phase values of the PACF of m-sequences (after mapping to a bipolar sequence) are all -1: Example: m-sequence of length 15

22 Decimation of M-Sequences
Definition (decimation): Given a m-sequence bn, generate a new sequence cn by taking every q-th element form bn. Then cn is said to be a decimation by q of bn. If bn is generated by ma(x) with roots ai then cn is generated by maq(x) with roots aiq. If gcd(q, N) = 1 then cn is also a m-sequence. Example: N = 31 is prime therefore all decimations give m-sequences (some of which may be identical !!)

23 Crosscorrelation Properties of Gold-Sequences
If L is not 0 mod 4 then pairs of m-sequences exist with three-valued crosscorrelation functions (CCF) these three values are: -1, -t(L), t(L)-2 its called preferred pair !

24 Construction of Gold Codes
A set of Gold codes of length N is generated based on a preferred pair of m-sequences of the same length. The second m-sequence is generated from the first by decimation with the factor t(L). The set size is N+2 = 2L+1. N different sequences in the set are generated by the binary addition of sequence 1 with all cyclic shifts of sequence 2. The original sequences are added to the set giving a set size of N+2. LFSR for m-sequence 2 m-sequence 1 Gold code initial value determines output sequence

25 Correlation properties of Gold Codes
Gold codes have three valued out of phase periodic autocorrelation function and even periodic crosscorrelation function: Example: Gold Codes of length N=31, L = 5, with Generator polynomials g1(x) = x5 + x and g2(x) = x5 + x4 + x2 + x + 1 The three out of phase correlation values are -1, -9 and 7

26 Segments of length 38460 of Gold codes of length 218-1 are used
in the WCDMA system (DL DPDCH/DPCCH). Example: Generator polynomials: g1(x) = x18 + x5 + x2 + x + 1 = m1(x) g2(x) = x18 + x17 + x13 + x12 + x9 + x8 + x6 + x + 1 = m1025(x) The second sequence is generated by decimating the first sequence with factor 2 (L+2)/2+1 = 1025.

27 Orthogonal Gold-Codes
For many Gold-Codes or Gold like codes of length 2L -1 the crosscorrelation value at phase 0 is -1. If these codes are suitably extended by one chip the crosscorrelation value at phase 0 is 0. Therefore the codes are orthogonal !! g1(x) = x8 + x6 + x5 + x and g2(x) = x8 + x4 + x3 + x2 + 1 Original codes have length 255. Orthogonal codes have length 256 by addition of the chip -1. Out of phase correlation properties change due to the extension bit. Example: L = 8

28 Correlation Properties of Gold like Codes of length 255

29 Correlation Properties of Orthogonal Gold-Codes of Length 256

30 Downlink scrambling code generator
X 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 In 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 Qn Y

31 spreading /modulation for downlink DPCH
16*2K kbps 3.84 Mcps cos(wt) p(t) IQ Mux DPDCH/DPCCH cch cscramb sin(wt) p(t) chiprate 3.84 Mcps pulse-shaping Root-Raised Cosine (RRC) with a=0.22 - QPSK modulation

32 spreading /modulation for uplink DPCH
Anpassungsfaktor chiprate 3.84 Mcps pulse-shaping Root-Raised Cosine (RRC) with a=0.22 - Dual BPSK modulation

33 RRC Impulse Response 0.4 0.35 0.3 0.25 0.2 0.15 0.1 0.05 -0.05 -0.1 10
-0.05 -0.1 10 20 30 40 50 60 70 80

34 Mapping of Transport Channels
Transport / Logical Channels Physical Channels BCH FACH PCH RACH CPCH DCH DSCH Common Pilot Channel Primary Common Control Physical Channel Secondary Common Control Physical Channel Physical Random Access Channel Physical Common Packet Channel Dedicated Physical Data Channel Dedicated Physical Control Channel Synchronization Channel Physical Downlink Shared Channel Page Indication Channel Acquisition Indication Channel Mapping of transport channels SCH consists of primary SCH and secondary SCH

35 Structure of Uplink Dedicated Channels
DPDCH Data1 Ndata bits DPCCH Pilot NTFCI bits TFCI Ts=2560 chips, 10*2k bits, k=0..7 FBI NFBI bits TPC NTPC bits slot #0 slot #1 slot #i slot #14 frame #0 frame #1 frame #i frame #71 Tf=10 ms Tsuper=720 ms Structure of uplink DPDCH and DPCCH DPDCH and DPCCH on the same Layer 1 Connection generally have different spreading factors, SFDPDCH=4..256, SFDPCCH=256 length of TFCI field can be 0 for fixed rate services support of TFCI mandatory for UE

36 Structure of Downlink Dedicated Channels
Pilot Npilotbits TFCI NTFCI bits TPC NTPC bits Data1 Ndata bits Data2 Ts=2560 chips, 10*2kbits, k=0..7 DPCCH DPDCH slot #0 slot #1 slot #i slot #14 frame #0 frame #1 frame #i frame #71 Tf=10 ms Tsuper=720 ms Structure of downlink dedicated channels SF is fixed, normally DTX is used length of TFCI field can be 0 for fixed rate services, determined by UTRAN support of TFCI mandatory for UE in closed loop transmit diversity the pilot symbol sent by different antennas are orthogonal

37 Multicode Downlink Transmission
Pilot TFCI TPC DPCH1 Data1 Data2 Transmission Power DPCH2 Data1 Data2 DPCHn Data1 Data2 Multicode downlink transmission only on DPCH carries the DPCCH

38 Multicode Uplink Transmission
DPDCH1 Data DPDCH2 Data DPDCHn Data Multicode uplink transmission there is only on DPCCH for each connection DPCCH Pilot TFCI FBI TPC

39 coding and multiplexing of Transport Channels (TC)
The output after inner (intra-frame ) interleaving is typically mapped to one DPDCH. Only for highest bit rates the output is mapped to several DPDCHs (multi-code transmission)

40 Convolutional coder

41 Random Access Transmission
P1 Pj P0 Preamble 4096 chips 10 ms, chips Message Random Access Transmission several preambles are transmitted with increasing power the preambles consists of 256 repetitions of a signature preamble transmission starts at random access slots If power is sufficient, BS sends an acquisition indication on AICH

42 RACH Message Part Data Control Pilot NTFCI bits TFCI Ndata bits
slot #0 slot #1 slot #i slot #14 Ts=2560 chips, 10*2kbits, k=0..3 TRACH=10 ms RACH message part SFdata = 256,128,64,32 SFcontrol = 256 Npilot = 8, NTFCI = 2

43 Acquisition Indication Channel
4096 chips 1024 chips AI empty AS #0 AS #1 AS #i AS #14 2*Tf=20 ms Acquisition Indication Channel Access slots are separated by 5120 chips AIi corresponds to a signature i on PRACH or PCPCH Aii is 16 symbol long for PCPCH: AP-AICH, CD-AICH phase reference for AICH is the CPICH

44 Timing relationrelationship between preambles, AICH message
One access slot t p-a p-m p-p Pre- amble Message part Acq. Ind. AICH access slots RX at UE PRACH access slots TX PRACH/AICH timing relation p-p  p-p,min. when AICH_Transmission_Timing is set to 0, then - p-p,min = chips (3 access slots) - p-a = 7680 chips - p-m = chips (3 access slots) when AICH_Transmission_Timing is set to 1, then - p-p,min = chips (4 access slots) - p-a = chips - p-m = chips (4 access slots)

45 Pre-defined symbol sequence
Common Pilot Channel Pre-defined symbol sequence NTFCI bits Ts=2560 chips, 10*2kbits, k=0..7 slot #0 slot #1 slot #i slot #14 frame #0 frame #1 frame #i frame #71 Tf=10 ms Tsuper=720 ms Common pilot channel (CPICH) all symbols of the pre-defined symbol sequence are 1+j in case of transmit diversity a different symbol sequence is sent by antenna 2

46 Primary Common Pilot Channel
Characteristics of the primary common pilot channel The same channelization code is always used Scrambled by the primary scrambling code One per cell Broadcast over entire cell The primary common pilot channel is the phase reference for SCH, P-CCPCH, AICH, PICH and the default phase reference for all other downlink physical channels. Primary Common Control Physical Channel fixed rate (30kbps,SF=256) carries BCH

47 Secondary Common Pilot Channels
Characteristics of the secondary common pilot channel usage of an arbitrary channelization code of SF=256 scrambled by either the primary or secondary scrambling code zero, one or several per cell may be transmitted over only a part of the cell A secondary common pilot channel may be the phase reference for the secondary CCPCH and the downlink DPCH

48 Synchronization Channel
Slot #0 Slot #1 Slot #14 Primary SCH acp acp acp Secondary SCH acsi,0 acsi,1 acsi,14 256 chips 2560 chips Synchronisation Channel primary and secondary SCH are modulated by a symbol a, a=+1 if P-CCPCH is STTD encoded, else a=-1 SCH is transmitted during TX off period of P-CCPCH P-SCH consists of the primary synchronization code (PSC), which length is 256 chips PSC is the same for every cell S-SCH consists of a sequence of 15 repeatedly transmitted codes (SSC) the sequence of the SSC determines, which of the code groups the cell belongs to 1 frame, 10 ms, chips

49 Physical Downlink Shared Channel
Data Ndata bits Ts=2560 chips, 20*2kbits, k=0..6 slot #0 slot #1 slot #i slot #14 frame #0 frame #1 frame #i frame #71 Tf=10 ms Tsuper=720 ms Physical Downlink Shard Channel Shard by users based on code multiplexing DSCH always associated with a DCH PDSCH always associated with a downlink DPCH PDCH does not have layer 1 control information control information is transmitted on DPCCH A DSCH may be mapped on multiple parallel PDSCHs

50 Power control (1) Outer loop (closed loop) adjust SIR target for inner loop Inner loop (closed loop) SIR controlled user oriented for fast Power Control Open loop for RACH

51 Power control (2)

52 Power control - inner loop
adjust TX power of BS and MS to reduce near-far effect Example (DL): MS estimates received power SRX of DPCCH after Rake combining MS estimates downlink interference IDL SIRest = SRX / IDL generate transmit power control (TPC) command according to SIRest > SIRtarget,DL ----> TPC = down SIRest < SIRtarget,DL ----> TPC = up BS increases power by DTPC dBs

53 Power control - TPC generation
BS: all base stations in the active set send TPC commands based on a quality measurement BS: threshold for TPC is controlled in the outer loop by the network node MS: power up if TPC bits received of all BS indicate an upward step MS: power down if TPC bits received of at least one BS indicate downward step

54 Power control - open loop (1)
Control RACH TX power uses pathloss SIR target broadcast by BCCH Uplink interference level broadcast by BCCH transmit power of CCPCH

55 Handover concept SNR estimation[dB] Active set replace hyteresis A
hysteresis threshold B C Time A connected Add B to active set Replace B Replace C Remove A with C with B

56 random data source FEC + rate matching + interleaving OVS long scrambling sampling rate expansion RRC-filter nonlinear PA Pilot TPC TFCI M U X channel searcher Rake de-interleaving + FEC decoding detection D E AWGN Goldcodes 64 groups a 8 codes Length = 38640 QPSK symbol scaling PC DAC decimation 1 2 3 4 5 6 7 8 9 10 11 12 13 15 16 17 21 23 24 27 22 26 29 30 31 BER calculation 28 analog Tx-filter 14 optional ADC 20 18 Rx-filter 19 25 P/S 32 TPC evaluation SIR Target

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