2
Outlines
Last Lecture Review
Spreading and Scrambling
Transport Channels
Physical Channels
►UL Dedicated
Signalling
Physical Layer Procedures
►RACH Operation
►Cell Searching
►Power Control
• Open Fast loop
• Closed Loop
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Air Interface Parameters-Wireless Networks-Lecture Slides, Slides of Wireless Networking
This course consist on introduction to wireless communication, evolution of wireless communication systems, medium access techniques, propagation models, error control techniques, cellular systems, emerging networks. This lecture inlcudes: Amps, Air, Signal, Introduction, Handling, Call, System, Band, User, Cell, Omin, Direction, Allocate
Typology: Slides
2011/2012
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Outlines
^ Last Lecture Review ^ Spreading and Scrambling ^ Transport Channels ^ Physical Channels^ ►^ UL Dedicated ^ Signalling ^ Physical Layer Procedures^ ►^ RACH Operation^ ►^ Cell Searching^ ►^ Power Control•^ Open Fast loop•^ Closed Loop
Last Lecture Review
^ Last Lecture review ^ UMTS ^ Service Classes in UMTS ^ UTRAN Architecture ^ Radio Interface protocol Architecture ^ Protocol Models for UTRAN ^ Logical Channels
Spreading and Scrambling Spreading means increasing the signal bandwidth Strictly speaking, spreading includes two operations: ► Channelization (increases signal bandwidth) - using orthogonalcodes ► Scrambling (does not affect the signal bandwidth) - usingpseudo noise
Channelization
^ Channelisation codes are orthogonal codes, based onOrthogonal Variable Spreading Factor (OVSF)technique ^ The codes are fully orthogonal, i.e., they do notinterfere with each other, only if the codes are timesynchronized ^ Thus, channelization codes can separate thetransmissions from a single source ^ In the downlink, it can separate different users withinone cell/sector ^ Limited orthogonal codes must be reused in every cell^ ►^ Problem: Interference if two cells use the same code^ ►^ Solution: Scrambling codes to reduce inter-base-stationinterference
Channelization
Scrambling
^ In the scrambling process the code sequence ismultiplied with a pseudorandom scrambling code. ^ The scrambling code can be a long code (a Gold codewith 10 ms period) or a short code (S(2) code). ^ In the downlink scrambling codes are used to reducethe inter-basestation interference. Typically, each NodeB has only one scrambling code for UEs to separatebase stations. Since a code tree under one scramblingcode is used by all users in its cell, proper codemanagement is needed.
Transport Channels -> Physical Channels ^ Transport channels contain the data generated at thehigher layers, which is carried over the air and aremapped in the physical layer to different physicalchannels. ^ The data is sent by transport block from MAC layer tophysical layer and generated by MAC layer every 10ms. ^ The transport format of each transport channel isidentified by the Transport Format Indicator (TFI),which is used in the interlayer communication betweenthe MAC layer and physical layer. ^ Several transport channels can be multiplexed togetherby physical layer to form a single Coded CompositeTransport Channel (CCTrCh).
^ The physical layer combines several TFI informationinto the Transport Format Combination Indicator(TFCI), which indicate which transport channels areactive for the current frame. ^ Two types of transport channels:
dedicated^ channels and^ common^
channels. ►^ Dedicated channel –reserved for a single user only.•^ Support fast power control and soft handover. ►^ Common channel – can be used by any user at any time.•^ Don’t support soft handover but some support fast power control. In addition to the physical channels mapped from thetransport channels, there exist physical channels for^ signaling^ purposes to carry only information betweennetwork and the terminals.
UL Dedicated Channel DCH Due to audible interference to the audioequipment caused from the discontinuous ULtransmission, two dedicated physical channelsare ► Dedicated Physical Control Channel (DPCCH) ► Dedicated Physical Data Channel (DPDCH) code multiplexing instead of time multiplexingto overcome discontinuous transmission (DTX).
^ Dedicated Physical Control Channel (DPCCH) has a fixedspreading factor of 256 and carries physical layer controlinformation. ^ DPCCH has four fields: Pilot, TFCI, FBI, TPC.^ ►^ Pilot – channel estimation + SIR estimate for PC^ ►^ TFCI – bit rate, channel decoding, interleaving parameters for everyDPDCH frame^ ►^ FBI (Feedback Information) – transmission diversity in the DL^ ►^ TPC (Transmission Power Control) – power control command
UL receiver in BS
^ It performs following^ ►^ Start receiving the frame, de-spreading DPCCH and bufferingthe DPDCH according to max bit rate corresponding to thesmallest spreading factor^ ►^ For every slot•^ Obtain channel estimate using pilot bits and estimate SIR•^ Send TPC command in DL to UE to control UL tx power•^ Decode TPC bit in every slot and adjust DL power for that UE^ ►^ For every 2
nd^ th^ or 4^ slot• Decode FBI bits, if present in 2 or 4 slots and adjust antennaphases and amplitude for transmission diversity ► For every 10 ms frame• Decode TFCI information from DPCCH frame to obtain bit rate ► For transmission time interval (TTI) of 10, 20, 40 or 80 ms,decode DPDCH data
UL Multiplexing and Channel Coding
Chain
Synchronisation Channel (SCH) – Cell
Searching ^ Cell search using SCH has three basic steps:^ ►^ The UE searches the 256-chip primary synchronisation code,which is common to all cells and is the same in every slot.Detect peaks in the output of the filter corresponds to the slotboundary (slot synchronisation).^ ►^ The UE seeks the largest peak secondary synchronisationcode (SSC). There are 64 unique SSC sequences. Each SSCsequence has 15 SSCs. The UE needs to know 15 successiveSSCs from the S-SCH, then it can determine the code group inorder to know the frame boundary (frame synchronisation).^ ►^ Each code group has 8 primary scrambling. The correct one isfound by each possible scrambling code in turn over theCPICH of that cell.
SSC Sequence Secondary Synchronization Code (SSC) and Code Group
Code group^ #0^ #^
#2^ #3^ #4^ #5^ #^
#7^ #8^ #9^ #10^
#12^ #13^
...^16 6 9 16 13
Start Frame^