3G Evolution Chapter 17 – Outline 17 Chapter: • The Uplink physical resource • Uplink reference signals • Uplink L1/L2 control signaling Uplink transmission scheme • Uplink transport-channel processing • PUSCH frequency hopping Department of Electrical and Information Technology Telmo Santos May 13, 2009 3G Evolution - HSPA and LTE for Mobile Broadband 3G Evolution - HSPA and LTE for Mobile Broadband 1 May 13, 2009 3G Evolution - HSPA and LTE for Mobile Broadband 2 17.1 The uplink physical resource 17.1 The uplink physical resource • Based on DFTS-OFDM transmission • Frequency domain structure – Low-PAR ’single-carrier’ transmission – Flexible bandwidth: 6–110 resource blocks (1–20 MHz ) – Flexible bandwidth assignment – Orthogonal multiple access in time and frequency No unused DC-subcarrier DFT size limited to products is defined for uplink of integers of 2,3 or 5 May 13, 2009 3G Evolution - HSPA and LTE for Mobile Broadband 3 May 13, 2009 3G Evolution - HSPA and LTE for Mobile Broadband 4
17.1 The uplink physical resource 17.2 Uplink reference signals • Time domain structure • Uplink demodulation reference signals (DRS) – Normal CP: 5.1us (1.5Km) 1 slot = 7 OFDM symbols – Necessary for demodulation – Time multiplexed – Extended CP: 16.7us (5Km) 1 slot = 6 OFDM symbols of PUSCH and PUCCH ( downlink: frequency multiplexed ) May 13, 2009 3G Evolution - HSPA and LTE for Mobile Broadband 5 May 13, 2009 3G Evolution - HSPA and LTE for Mobile Broadband 6 17.2 Uplink reference signals 17.2 Uplink reference signals • Uplink DRS should have the following properties • So why are we not using Zadoff-Chu sequences directly? – Limited power variations in the frequency domain to allow for similar – Prime-length ZC sequences are preferred to maximize the number of channel-estimation quality for all frequencies. possible number of sequences. But, the reference-signals length must be a multiple of 12. – Limited power variations in the time domain to allow for high power-amplifier efficiency. – For short sequence lengths, relatively few sequences would be available. • For sequence lengths >= 36: Sounds contradicting? maybe not... we use cyclic extensions of shorter prime-length sequences (freq.domain) Zadoff-Chu sequences: 36 A minimum of 30 sequences 31 (30 diff. seq.) must exist for each length! Constant power in both the • For sequence lengths of 12 or 24: frequency and the time domain 30 QPSK-based sequences were found from computer search May 13, 2009 3G Evolution - HSPA and LTE for Mobile Broadband 7 May 13, 2009 3G Evolution - HSPA and LTE for Mobile Broadband 8
17.2 Uplink reference signals 17.2 Uplink reference signals • Phase-rotated reference-signal sequences • Possible uses for phase-rotated (orthogonal) reference- signal sequences PUCCH PUSCH Frequency domain Time domain = phase rotation cyclic shift eNodeB user Root sequence (in time-domain): • Multiple mobile terminals within a cell simultaneously use the same and the They are perfectly Phase-rotated sequences: • Reduced intercell interference frequency resource good thing is: orthogonal! (requires good time alignment between neighour cells uplink and are different phase rotations transmission) May 13, 2009 3G Evolution - HSPA and LTE for Mobile Broadband 9 May 13, 2009 3G Evolution - HSPA and LTE for Mobile Broadband 10 17.2 Uplink reference signals 17.2 Uplink reference signals • Reference-signal assignment to cells • Reference-signal assignment to cells (cont.) – At least we must have 30 sequences per sequence length. – Fixed group assignment Length <= 60 Length => 72 PUCCH PUSCH Sequence group given by the Sequence group is explicitly signaled physical layer cell identity as part of the cell system modulo 30. information. Cell identity ranges from 0 to 503. This enables the possibility for neighour cells to share the same sequence group (slide 9). – Group hopping The group hopping pattern is defined from the cell identity. In a given time slot, the uplink reference-signal Bandwidth measured in number sequences in a cell are taken from one group, of resource blocks must be – Sequence hopping which can be: a product of 2, 3 or 5! Optional scheme to be used for sequence lengths corresponding to 6 resource fixed group assignment or group hopping blocks and above May 13, 2009 3G Evolution - HSPA and LTE for Mobile Broadband 11 May 13, 2009 3G Evolution - HSPA and LTE for Mobile Broadband 12
17.2 Uplink reference signals 17.2 Uplink reference signals • Uplink sounding reference signals (SRS) • Uplink sounding reference signals (SRD) – These are transmitted to allow for the network to estimate the uplink – SRS should cover the bandwidths of interest for the frequency-domain channel quality at different frequencies. scheluding. – Not necessarily transmitted together with any physical channel. – Transmitted in regular intervals, from • 2ms (every second subframe) • 160ms (every 16th subframe) Always a multiple of 4 RB To avoid collision between SRS and PUSCH transmissions, no terminals use the last DFTS-OFDM symbol of those subframes for PUSCH. May 13, 2009 3G Evolution - HSPA and LTE for Mobile Broadband 13 May 13, 2009 3G Evolution - HSPA and LTE for Mobile Broadband 14 17.2 Uplink reference signals 17.3 Uplink L1/L2 control signaling • Uplink sounding reference signals (SRD) • It consist of – Also based on Zadoff-Chu sequences. – Hybrid ARQ acknowledgements – Sequence mapped to every second subcarrier – Reports of channel conditions to help downlink scheduling – Scheduling requests for UL-SCH transmissions • Other characteristics ≠ from downlink – Information on uplink indicating the UL-SCH transport-format Different rotations require the (it has already been defined by eNodeB). span of the same bands. – It is always transmitted regardless if the terminal has been assigned uplink resources for UL-SCH or not. No simultaneous Simultaneous Different combinations allow transmission of UL-SCH transmission of UL-SCH the span of different bands. (transmission over PUCCH) (transmission over PUSCH) May 13, 2009 3G Evolution - HSPA and LTE for Mobile Broadband 15 May 13, 2009 3G Evolution - HSPA and LTE for Mobile Broadband 16
17.3 Uplink L1/L2 control signaling 17.3 Uplink L1/L2 control signaling • Uplink L1/L2 control signaling on PUCCH • PUCHH format 1 – Hybrid ARQ acknowledgements – Scheduling requests Resources are transmitted on the edges of the available cell bandwidth • Reasons to use the edges of the spectrum – Maximize frequency diversity • 3 symbols for channel estimation – Not to block the assignment of very large bandwidths to a single terminal Terminals can be separated by rotated sequences and cover sequences • 4 symbols for BPSK/QPSK mod May 13, 2009 3G Evolution - HSPA and LTE for Mobile Broadband 17 May 13, 2009 3G Evolution - HSPA and LTE for Mobile Broadband 18 17.3 Uplink L1/L2 control signaling 17.3 Uplink L1/L2 control signaling • PUCHH format 1 • PUCHH format 1 – Scheduling requests – Inter-cell interference exists from the non orthogonal neighboring – Occurrences of hybrid-ARQ ack. are well known to the eNodeB sequences. – However, the need for uplink resources for a certain terminal is in principle Cell A Cell B unpredicatble by eNodeB Considerig: • 6 rotations (out of 12) Every terminal is given a reserved resource on which it can transmit a • 3 cover sequences request for uplink. we get 18 possible terminals. LTE provides a contention-free scheduling request mechanism. No collisions! This helps randomizing the inter-cell interference May 13, 2009 3G Evolution - HSPA and LTE for Mobile Broadband 19 May 13, 2009 3G Evolution - HSPA and LTE for Mobile Broadband 20
17.3 Uplink L1/L2 control signaling 17.3 Uplink L1/L2 control signaling • PUCHH format 2 • Simultaneous transmission of multiple feedback reports PUCHH format 2 is capable of multiple – Channel status reports – Hybrid-ARQ acknowledgement and channel-status report information bits per subframe Per subframe we have: • 4 symbols for channel estimation • 10 symbols for QPSK mod Rotation angles are also hopping to randomize inter-cell interference May 13, 2009 3G Evolution - HSPA and LTE for Mobile Broadband 21 May 13, 2009 3G Evolution - HSPA and LTE for Mobile Broadband 22 17.3 Uplink L1/L2 control signaling 17.3 Uplink L1/L2 control signaling • Resource-block mapping for PUCCH • Uplink L1/L2 control signaling on PUSCH – Multiple resource block pairs can be used to increase the control-signaling – Control signaling is time multiplexed with the data on the PUSCH. capacity. PUCCH format 1 and 2 Hybrid-ARQ ack. is multiplexed over different simply punctured into the phase rotations coded UL-SCH bit stream Rate matching not needed Hybrid-ARQ ack. is given special attention due to its importance PUCCH format 2 is put on the edges of the cell bandwidth May 13, 2009 3G Evolution - HSPA and LTE for Mobile Broadband 23 May 13, 2009 3G Evolution - HSPA and LTE for Mobile Broadband 24
Recommend
More recommend
