Mobile Comms. Systems. Radio Interface

Transcription

1 Radio Interface

2 Multiple Access Techniques MuAT (1/23) The transmission of bidirectional information in duplex systems (uplink - UL - and downlink - DL - channels) can be done by dividing in: frequency: UL and DL channels occupy different frequency bands FDD (Frequency Division Duplex); time: UL and DL channels occupy different time windows TDD (Time Division Duplex).

3 Multiple Access Techniques MuAT (2/23) FDD is characterised by: allowing simultaneous transmission in both ways; requiring filters with a good rejection in the adjacent band; requiring, in general, the use of duplex filters. UL DL [Source: Rappaport, 1996]

4 Multiple Access Techniques MuAT (3/23) TDD is characterised by: doing a sequential transmission in both ways; requiring synchronism; not requiring duplex filters. UL DL [Source: Rappaport, 1996]

5 Multiple Access Techniques MuAT (4/23) The use of a duplex division technique may depend on the multiple access technique used for the system. In order to have efficient systems, each user should have a channel allocated to him/her only when it is requested, and when it is needed.

6 Multiple Access Techniques MuAT (5/23) There are 3 basic multiple access techniques: frequency: allocation of a carrier FDMA (Frequency Division Multiple Access) time: allocation of a time-slot TDMA (Time Division Multiple Access) code: allocation of a code CDMA (Code Division Multiple Access)

7 Multiple Access Techniques MuAT (6/23) FDMA is the classic scheme, used in analogue systems, in which each user occupies a carrier during the connection. [Source: Rappaport, 1996]

8 Multiple Access Techniques The main characteristics of FDMA are: single channel per carrier; continuous transmission; low inter-symbol interference; low information overhead; simple user equipment; high BS cost; use of duplex filters; perceptible handover. MuAT (7/23)

9 Multiple Access Techniques MuAT (8/23) In TDMA, each user has access to the whole band, a time-slot being periodically allocated to him/her, in a frame structure. [Source: Rappaport, 1996]

10 Multiple Access Techniques MuAT (9/23) TDMA requires the use of a hierarchy of frames and time-slots. [Source: Rappaport, 1996]

11 Multiple Access Techniques The main characteristics of TDMA are: multiple channels per carrier; burst transmission; synchronism required; narrow- or wideband systems; high inter-symbol interference; high information overhead; complex user equipment; low BS cost; duplex filters not required; efficient handover. MuAT (10/23)

12 Multiple Access Techniques Time-slots synchronism is essential. MuAT (11/23) [Source: Shankar, 2002]

13 Multiple Access Techniques MuAT (12/23) CDMA is based on a spread spectrum technique, in which each user has access to a code. [Source: Rappaport, 1996]

14 Multiple Access Techniques User s information is associated to a code: the transmission scheme is MuAT (13/23) [Source: Yacoub, 1992]

15 Multiple Access Techniques in transmission, one has MuAT (14/23) [Source: Shankar, 2002]

16 Multiple Access Techniques the reception scheme is MuAT (15/23) [Source: Yacoub, 1992]

17 Multiple Access Techniques in reception, one has MuAT (16/23) [Source: Shankar, 2002]

18 Multiple Access Techniques CDMA leads to a high increase in bandwidth. MuAT (17/23) [Source: Shankar, 2002]

19 Multiple Access Techniques MuAT (18/23) The main characteristics of CDMA are: unlimited channels per carrier; (very) wide bandwidth; very high inter-symbol interference; interference and capacity are user dependent; low sensitivity to fast fading; power control is essential; low (control) information overhead; still a new technology.

20 Multiple Access Techniques GSM uses TDMA MuAT (19/23) [Source: Yacoub, 2002]

21 Multiple Access Techniques GSM s time-slot structure is: MuAT (20/23) [Source: Yacoub, 2002]

22 Multiple Access Techniques UMTS uses CDMA, with 2 types of codes: channelisation; scrambling. MuAT (21/23) Channelisation code Scrambling code Data Bit rate Chip rate Chip rate

23 Duration Number Multiple Access Techniques The two codes have different functionalities. Channelisation Scrambling Use DL: MT DL: sector separation separation UL: channel UL: MT separation Family OVSF Spreading Yes 1 chip = ns separation DL: chip UL: chip Spreading factor chip MuAT (22/23) DL: 512 UL: > Gold or S(2) No

24 Multiple Access Techniques MuAT (23/23) The OVSF (Orthogonal Variable Spreading Factor) code tree defines the spreading. SF = 1 SF = 2 SF = 4 SF = 2 k, k = 2,3,..., 16 [Source: Holma and Toskala, 2004]

25 Channel Description ChDe (1/23) There are 3 basic types of channels: radio channel: channel associated to a carrier frequency; physical channel: channel transporting any kind of system information, associated to a carrier, time-slot, or code; logical channel: channel transporting a specific kind of system information.

26 Channel Description ChDe (2/23) Concerning content, one distinguishes: traffic channels: contain users information, e.g., voice, data, and video; control channels: contain system s information, e.g., signalling, synchronism, control, and identity. Concerning addressing, one distinguishes: common channels: exchange of information between the BS and TMs in general; dedicated channels: exchange of information between the BS and one or several (specific) TMs.

27 Channel Description ChDe (3/23) Radio channels: come from the division of the spectrum band into N rc intervals; are separated by Δf cs ; have a bandwidth of Δf rc. f c -1 c-1 f c f c+1 c +1 Δf rc lb cr Δfcs Δfcs f Δf sc Δf sc

28 Channel Description GSM radio channels have: Δf cs = 200 khz Δf rc = 200 khz with 900 MHz band UL: [890, 915] MHz DL: [935, 960] MHz 1800 MHz band UL: [1 710, 1 785] MHz DL: [1 805, 1 880] MHz ChDe (4/23)

29 Channel Description GSM radio channels mask: ChDe (5/23) BS:20W BS:2W MT:5W MT:2W [Source: Steele, 1992]

30 Channel Description GSM radio channels spectrum: ChDe (6/23) [Source: Mouly and Paulet, 1992]

31 Channel Description ChDe (7/23) UMTS radio channels have: Δf cs = 5 MHz Δf rc = 4.4 MHz with FDD mode UL: [1 920, 1 980] MHz DL: [2 110, 2 170] MHz TDD mode UL/DL: [1 900, 1 920] [2 010, 2 025] MHz

32 Channel Description UMTS radio channels spectrum: ChDe (8/23) [Source: Lempiäinen and Manninen, 2001]

33 Channel Description ChDe (9/23) Physical channels transport information in the radio interface, depending on the type of multiple access: in analogue systems, they correspond to radio channels; in GSM, they correspond to time-slots in a carrier; in UMTS, they correspond to codes with different characteristics, depending on the link way.

34 Channel Description ChDe (10/23) UMTS physical channels are: DL: P-CCPCH Primary Common Control Physical Channel S-CCPCH Secondary Common Control Physical Channel DPDCH Dedicated Physical Data Channel DPCCH Dedicated Physical Control Channel PDSCH Physical Downlink Shared Channel

35 Channel Description ChDe (11/23) UL: PRACH Physical Random Access Channel DPDCH Dedicated Physical Data Channel DPCCH Dedicated Physical Control Channel PCPCH Physical Common Packet Channel

36 Channel Description In UMTS, the scheme of physical channels is: ChDe (12/23) MT P-CCPCH S-CCPCH DPDCH DPCCH PDSCH PCPCH PRACH BS

37 Channel Description ChDe (13/23) Logical channels are associated to traffic and control contents, defining the transfer of a specific type of information between the MT and the network. The complexity of logical channels has been increasing along the several generations.

38 Channel Description ChDe (14/23) GSM logical channels are: TCH Traffic Channels (UL/DL): CS TCH-S Speech (11.4, 22.8 kb/s) TCH-D Data (9.6, 4.8, 2.4 kb/s) PS (GPRS) PDTCH Packet Data Traffic Channel

39 Channel Description ChDe (15/23) CCH Control Channels: BCCHs Broadcast Control Channels BCCH Broadcast Control Channel (DL) FCCH Frequency Correction Channel (DL) SCH Synchronisation Channel (DL) CCCH Common Control Channels PCH Paging Channel (DL) AGCH Access Grant Channel (DL) RACH Random Access Channel (UL)

40 Channel Description ChDe (16/23) DCCH Dedicated Control Channels (UL/DL) SDCCH Stand-alone Dedicated Control Channel FACCH Fast Associated Control Channel SACCH Slow Associated Control Channel

41 Channel Description In GSM, the scheme of logical channels is: ChDe (17/23) MT TCH BCCHs CCCH PCH AGCH RACH DCCH BS

42 Channel Description ChDe (18/23) UMTS logical channels are: BCCH Broadcast Control Channel (DL) PCCH Paging Control Channel (DL) CCCH Common Control Channel (UL/DL) CTCH Common Traffic Channel (DL) DCCH Dedicated Control Channel (UL/DL) DTCH Dedicated Traffic Channel (UL/DL)

43 Channel Description In UMTS, the scheme of logical channels is: ChDe (19/23) MT BCCH PCCH CCCH CTCH DTCH DCCH BS

44 Channel Description ChDe (20/23) In UMTS, transport channels establish the interface between the UE and the RNC. UE Node B RNC Logical Channels Transport Channels Physical Channels

45 Channel Description UMTS transport channels are: DL BCH Broadcast Channel PCH Paging Channel FACH Forward Access Channel DCH Dedicated Channel (UL/DL) DSCH Dedicated Shared Channel UL RACH Random Access Channel DCH Dedicated Channel (UL/DL) CPCH Common Packet Channel ChDe (21/23)

46 Channel Description UMTS DL channel mapping is: BCCH PCCH CTCH CCCH DCCH ChDe (22/23) DTCH Logical channels BCH PCH FACH DCH DSCH Transport channels P- CCPCH S- CCPCH DPDCH DPCCH PDSCH Physical channels

47 Channel Description while in UL: CCCH DTCH DCCH ChDe (23/23) Logical channels RACH DCH CPCH Transport channels PRACH DPDCH DPCCH PCPCH Physical channels

48 Comparison SyCo (1/5) One can consider that the transition between GSM (2nd generation system) and UMTS (3rd generation system) was done through cdmaone (2nd generation system) in the USA, by introducing CDMA.

49 Comparison SyCo (2/5) GSM cdmaone UMTS Access Chan. [MHz] Reference service Shared resource Channels per service Power control [Hz] Packet transmission TDMA 0.2 Voice Frequency Mono 2 GPRS CDMA 1.25 Voice Power Mono 800 Based on CS CDMA 5 Data Power Multi Based on codes

50 Comparison SyCo (3/5) cdmaone UMTS Chip rate [Mc/s] Frame [ms] BSs synchronism Inter-frequency handover Sensitivity to Radio Resource Management Yes (via GPS) Possible No (voice) No Yes High, associated to QoS

51 Comparison SyCo (4/5) Frequency reuse Physical channels Power per channel Frequency diversity Planning Sensitivity to planning Quality measure Coverage/capacity trade-off. GSM 3-12 Time-slots Dedicated Slow freq. hopping Frequencies High Frequency planning No UMTS 1 Codes Shared Wideband Codes Low Radio Resource Management yes

52 Comparison SyCo (5/5) Access Duplex Band Total bandwidth Chip rate [Mc/s] Spreading Factor Multi bit rate Handover UMTS Mode FDD Mode TDD WCDMA (FDMA) TDMA/CDMA (FDMA) FDD TDD Paired Unpaired 2 60 MHz 35 MHz , ,..., 512 1,..., 16 Multi-code, OVSF Multi-code, multi-slot, OVSF Soft/Hard Hard

53 Table of Contents MuAT - Multiple Access Techniques ChDe - Channel Description SyCo - Comparison ToC (1/1)