High performance NLOS wireless backhaul frame structure

Abstract

To provide a method for improving backhaul transmission in a wireless NLOS (Non-Line-Of-Sight) environment.SOLUTION: A wireless communication system includes a small cell site 504 and a macro cell site 508, in which the small cell site 504 includes a small cell BTS 514, in which the small cell BTS 514 communicates with a legacy UE 500 via an LTE link 502. A method of operating the wireless communication system includes communicating by a backhaul link 506 having a first transmit time interval with the small cell site 504 and communicating by an LTE link 502 having a second transmit time interval different from the first transmit time interval with the UE 500. Data is transferred between the backhaul link 506 and the LTE link 502.SELECTED DRAWING: Figure 5B

Description

Technical Field

[0001] This application generally relates to wireless communication systems, and more specifically, to the transmission of a Non-Line-Of-Sight (NLOS) backhaul frame structure that is compatible with a Time Division Duplex Long Term Evolution (TD-LTE) radio access network (RAN).

Background Art

[0002] It is a common perception that the main countermeasure against the huge increase in data demand in cellular networks is typically the deployment of small cells that provide Long Term Evolution (LTE) connections to a smaller number of users than the number of users served by macro cells. This enables both providing users with larger transmission / reception resource opportunities and reducing the load on the macro network. However, while the technical challenges of the small cell radio access network (RAN) have been the focus of considerable standardization efforts through 3GPP Releases 10 to 12, little attention has been paid to the technical challenges of the backhaul. This is particularly a difficult technical challenge for outdoor small cell deployments where wired backhaul is usually not available. This is often due to non-conventional locations of small cell sites such as lamp posts, road signs, bus stops, etc., in which case wireless backhaul is the most practical solution.

[0003] LTE wireless access technology, also known as E-UTRAN (Evolved Universal Terrestrial Radio Access Network), was standardized by a 3GPP working group. OFDMA and SC-FDMA (Single Carrier FDMA) access schemes were selected for the DL and UL of E-UTRAN, respectively. User Equipment (UE) is time and frequency multiplexed on the Physical Uplink Shared Channel (PUSCH) and Physical Uplink Control Channel (PUCCH), and time and frequency synchronization among UEs guarantees optimal inter-cell orthogonality. The LTE air interface provides the best spectral efficiency and the cost trade-off of recent cellular network standards, so it has been widely adopted by operators as a proprietary 4G technology for Radio Access Networks (RAN), making it a robust and proven technology. As described above and as shown in Figure 2, the trend in RAN topology is to increase cell density by adding small cells in the vicinity of traditional macrocells. Cellular macro site 200 hosts a macro base station. Macro site 200 also hosts small cell base stations and wireless backhaul hub units (HUs) located in the same place. Macro site 200 has small cell sites 204, 205, 207, and 208 under its umbrella, and each small cell site also hosts a small cell base station and a wireless backhaul remote unit (RU) located in the same place. Macro site 200 communicates with small cell sites 204, 205, 207, and 208 through a point-to-multipoint (P2MP) wireless backhaul system using wireless links 210, 211, 212, 213. The base station of macro site 200 communicates directly with UE206 via RAN link 230. However, UE202 communicates directly with the small cell base station of small cell site 204 via RAN access link 220. The RU of small cell site 204 communicates directly with the HU of macro site 200 via RAN backhaul link 210.This can cause significant inter-cell interference not only between the access link 220 and the backhaul link 210, but also between the backhaul link 210 and the access link 230 when both share the same frequency resources, as in the case of the RAN in a backhaul frequency reuse 1 scenario.

[0004] As the cell density increases with multiple RUs, the differences between the RAN and the backhaul wireless channel decrease. This requires a point-to-multipoint backhaul topology as shown in FIG. 2. As a result, conventional wireless backhaul systems that typically use single-carrier waveforms with time-domain equalization (TDE) techniques at the receiver are becoming less practical in these environments. This is mainly due to their limitations in operating in point-to-point line-of-sight (LOS) channels, for example, in the 6-42 GHz microwave frequency band. Also, this spectrum is already saturated with existing backhaul traffic, and higher frequencies such as the E-band and V-band are becoming very attractive for this type of link. However, these bands also come with their specific technical challenges such as high sensitivity to environmental conditions and require very tight beam pointing and tracking in operation. They are not yet developed enough to provide the level of robustness, flexibility, and low-cost requirements for small cell backhaul deployments. Rather, the similarity between small cell backhaul and small cell access topologies (P2MP) and the wireless wireless channel (LOS) naturally leads to the use of very similar air interfaces.

[0005] In wireless systems such as LTE, a base station and a wireless terminal or user equipment (UE) operate as a master-slave pair, respectively, and downlink (DL) and uplink (UL) transmissions are configured or scheduled by the base station. In LTE systems, a TTI is 1 ms long and has a subframe duration. Figure 1 shows LTE TDD UL / DL subframe configurations with different UL and DL allocations to support various mixes of UL and DL traffic ratios or to enable coexistence between different TDD wireless systems. For example, configuration 0 may provide eight UL subframes (U) including a special subframe (S). Configuration 5 may provide nine DL subframes (D) including a special subframe (S).

[0006] Several issues are associated with co-located time division duplex LTE (TD-LTE) RAN and backhaul links at small cell sites, including enabling highly integrated, cost-effective solutions. These include RAN and backhaul modems in the same box, or even in the same system-on-chip (SoC), providing self-configurable RAN and backhaul links. Also, sparse and costly spectrum leads to the sharing of the same band for access and backhaul transmission. Based on these, in-band LTE relaying was standardized as part of 3GPP Release 10, but is generally unsuitable due to its 1 ms subframe TTI, high block error rate (BLER), and high latency with high overhead.

[0007] While the preceding approaches provide improvements for backhaul transmission in wireless NLOS environments, further improvements are possible. Summary of the Invention

[0008] In the first embodiment, a method of operating a wireless communication system includes communicating with a first wireless transceiver by a first data frame having a first transmission time interval, and communicating with a second wireless transceiver by a second data frame having a second transmission time interval different from the first transmission time interval. Data is transmitted between the first data frame and the second data frame.

[0009] In the second embodiment, a method of operating a wireless communication system includes communicating with a first wireless transceiver by a first data frame having a first transmission time interval at a first time using a first frequency resource, either on the uplink or the downlink, and communicating with a second wireless transceiver by a second data frame having a second transmission time interval at the first time using the first frequency resource, either on the uplink or the downlink.

[0010] In the third embodiment, a method of operating a wireless communication system includes communicating with a second wireless transceiver by a first wireless transceiver using a first data frame having a first transmission time interval, either on the uplink or the downlink. The first data frame communicates data with a second data frame having a second transmission time interval different from the first transmission time interval at the second wireless transceiver, either on the uplink or the downlink, and the first and second data frames use the same carrier frequency.

Brief Description of the Drawings

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Best Mode for Carrying Out the Invention

[0026] Embodiments are directed to a NLOS time division duplex (TDD) wireless backhaul design for maximizing spectrum reuse. This design utilizes a 0.5 ms slot-based transmission time interval (TTI) for minimizing latency and a 5 ms UL and DL frame for compatibility with TD-LTE. Thus, various UL / DL ratios are compatible with the TD-LTE configuration (Figure 1). This enables flexible slot assignment for multiple remote units (RUs). A special slot structure is disclosed, which includes a synchronization signal (SS), a physical broadcast channel (PBCH), a pilot signal (PS), a guard period (GP), and a physical random access channel (PRACH), as will be described in detail later. These slot-based features greatly simplify the LTE frame structure, reduce costs, and maintain compatibility with TD-LTE. Exemplary embodiments advantageously use a robust forward error correction (FEC) method by concatenating a turbo code as an inner code with a Reed-Solomon outer block code that provides a very low block error rate (BLER). Also, embodiments support carrier aggregation with up to 4 CCs per HU by dynamic scheduling of multiple RUs with one dynamic assignment per component carrier (CC). These embodiments also support semi-persistent scheduling (SPS) of small allocations in frequency division multiple access (FDMA) within a slot for an RU designated to carry high priority traffic, thereby avoiding the latency associated with time division multiple access (TDMA) of dynamic scheduling. This combination of TDMA dynamic scheduling and FDMA SPS provides optimal performance with minimal complexity.

[0027] Throughout this specification, several of the following abbreviations are used. BLER: Block Error Rate CQI: Channel Quality Indicator CRS: Cell-Specific Reference Signal CSI: Channel State Information CSI-RS: Channel State Information Reference Signal DCI: Downlink Control Information DL: Downlink DwPTS: Downlink Pilot Time Slot eNB: E-UTRAN Node B or base station or eNode B EPDCCH: Enhanced Physical Downlink Control Channel E-UTRAN: Evolved Universal Terrestrial Radio Access Network FDD: Frequency Division Duplexing HARQ: Hybrid Automatic Repeat Request HU: (Backhaul) Hub Unit ICIC: Inter-Cell Interference Coordination LTE: Long Term Evolution MAC: Medium Access Control MIMO: Multiple-Input Multiple-Output MCS: Modulation and Coding Scheme OFDMA: Orthogonal Frequency Division Multiple Access PCFICH: Physical Control Format Indicator Channel PDCCH: Physical Downlink Control Channel PDSCH: Physical Downlink Shared Channel PRB: Physical Resource Block PRACH: Physical Random Access Channel PS: Pilot Signal PUCCH: Physical Uplink Control Channel PUSCH: Physical Uplink Shared Channel QAM: Quadrature Amplitude Modulation RAR: Random Access Response RE: Resource Element RI: Rank Indicator RRC: Radio Resource Control RU: (Backhaul) Remote Unit SC-FDMA: Single Carrier Frequency Division Multiple Access SPS: Semi-Persistent Scheduling SRS: Sounding Reference Signal TB: Transport Block TDD: Time Division Duplexing TTI: Transmission Time Interval UCI: Uplink Control Information UE: User Equipment UL: Uplink UpPTS: Uplink Pilot Time Slot

[0028] Figure 3 shows a TDD frame structure with seven UL / DL frame configurations and thus supports a diverse mix of UL and DL traffic ratios. In one embodiment, this frame structure is used to generate the NLOS backhaul link 210 of FIG. 2. However, exemplary embodiments can be used to generate any type of communication link that shares similar coexistence with TD-LTE and performance requirements such as those of the NLOS backhaul link. As a result, without loss of generality, the frame structure and associated components (slots, channels, etc.) are referred to as "NLOS backhaul" or simply "NLOS" frames, slots, channels, etc.

[0029] Referring to FIG. 4, the frame structure of a conventional 10 ms TD-LTE frame is compared with a 5 ms TDD frame (FIG. 5A). FIG. 4 is a more detailed view of UL / DL frame configurations 0 to 2 as shown in FIG. 1. FIG. 5A is a more detailed view of UL / DL frame configurations 1, 3, and 5 as shown in FIG. 3. The frame in FIG. 4 is divided into 10 subframes, and each subframe has a 1 ms TTI. Each subframe is further divided into 2 slots, and each slot has a period of 0.5 ms. Therefore, there are 20 slots (0 to 19) within each TD-LTE configuration. D in a certain slot indicates that it is a downlink slot. Similarly, U in a certain slot indicates that it is an uplink slot. Time slots 2 and 3 constitute a special subframe that enables the transition from a DL subframe to a UL subframe. DwPTS and UpPTS indicate the downlink and uplink portions of the special subframe, respectively.

[0030] In comparison, the frames in FIGS. 3 and 5A have a 5 ms period and are slot-based rather than subframe-based. Each frame has 10 slots (0 to 9). Each slot has a period of 0.5 ms. Similar to the frame in FIG. 4, D indicates a downlink slot and U indicates an uplink slot. However, in each of the three UL / DL configurations in FIG. 5A, slot 3 of both frames contains a special slot indicated by S rather than the special subframes in slots 2 to 3 and 12 to 13 in FIG. 4. This fixed position of the special slot guarantees compatibility with the TD-LTE frame. Advantageously, it always enables finding a NLOS UL / DL configuration that has 100% compatibility with any 5 ms period TD-LTE UL / DL subframe configuration. For example, this prevents NLOS backhaul DL transmission from interfering with TD-LTE RAN UL transmission on the access link when both operate at the same frequency. In other words, advantageously, it prevents the transmitter of macrocell site 200 of one system from interfering with the receiver of the system placed at the same location.

[0031] The frame structure of FIG. 5A has some common features with the frame structure of FIG. 4 to ensure compatibility when operating at the same frequency. Both frames have a 0.5 ms slot period with 7 SC-FDMA symbols and a normal cyclic prefix (CP) in each slot. The SC-FDMA symbol period is the same in each frame. Both frames have the same number of subcarriers for respective bandwidths of 5 MHz, 10 MHz, 15 MHz, and 20 MHz, and both have a 15 kHz subcarrier spacing. Both frames use the same resource element (RE) definition and support 4, 16, and 64 QAM modulation.

[0032] The frame structure of FIG. 5A has some unique features. The symbols in each slot are mainly SC-FDMA for both UL and DL. The first SC-FDMA symbol in each slot contains a pilot signal (PS) to improve system latency. A cell-specific synchronization signal (SS) different from the PS is included in each frame for cell search and frame boundary detection.

[0033] FIG. 5B shows a communication system according to an exemplary embodiment. The communication system includes a small cell site 504 and a macro cell site 508. The small cell site 504 includes a small cell BTS 514, and the small cell BTS 514 communicates with a legacy UE 500 via an LTE link 502 according to the frame structure of FIG. 4. The communication system further includes a backhaul hub unit (HU) 518, and the backhaul HU 518 may be co-located with a macro BTS or a base station 520 at the macro cell site 508. Alternatively, the backhaul hub HU may communicate with the macro BTS via a separate wireless link. A remote unit (RU) 516 is co-located with the small cell BTS 514 at the small cell site 504 and communicates with the HU 518 via a backhaul link 506 according to the frame structure of FIG. 5A. An uplink (UL) transmission from the RU 516 to the HU 518 is transmitted synchronously with a UL transmission from the UE 510 to the macro BTS 520. This synchronous transmission is aligned at the frame boundary and uses the same single carrier center frequency of the operating bandwidth. The UL transmission from the UE 510 to the macro BTS 520 is transmitted via the LTE link 512 according to the frame structure of FIG. 4. The UL transmission from the RU 516 to the HU 518 is transmitted via the backhaul link 506 according to the frame structure of FIG. 5A. Similarly, a downlink (DL) transmission from the HU 518 to the RU 516 is transmitted synchronously with a DL transmission from the macro BTS 520 to the UE 510. This synchronous transmission is aligned at the frame boundary and uses the same single carrier center frequency of the operating bandwidth. The DL transmission from the macro BTS 520 to the UE 510 is transmitted via the LTE link 512 according to the frame structure of FIG. 4. The DL transmission from the HU 518 to the RU 516 is transmitted via the backhaul link 506 according to the frame structure of FIG. 5A.

[0034] Figure 6 shows the configurations of 9 (0 - 8) 1 - ms TD - LTE special sub - frames. Figure 7 is a diagram of a 0.5 - ms NLOS special slot connected to a 0.5 - ms NLOS DL backhaul (BH) slot. The NLOS special slot includes DwPTS, UpPTS, and a guard period to achieve a 0.5 - ms period. As shown, the UL and DL transmissions of the NLOS backhaul slot always match the UL and DL transmissions of the TD - LTE slot, regardless of the TD - LTE special sub - frame configuration. Specifically, the DwPTS of the TD - LTE special sub - frame occurs simultaneously with the DL slot preceding the special slot of the NLOS frame and overlaps with the DwPTS of the NLOS special slot. Similarly, the UpPTS of the TD - LTE special sub - frame occurs simultaneously with the DwPTS of the NLOS special slot. Therefore, the NLOS BH special slot includes essential features of the TD - LTE special sub - frame to ensure compatibility when operating at the same frequency. Therefore, the NLOS frame and special slot structure enable simultaneous LTE access and backhaul transmission either in UL or DL. The simultaneous transmission occurs during the TTI of the UL or DL slot in FIGS. 4 - 5A and at the SC - FDMA symbol level in the respective special sub - frames and slots of FIGS. 6 and 7.

[0035] Figure 8 is a detailed diagram of the NLOS BH frame as shown in UL / DL configuration 3 of FIG. 5. Here, and in the following description, the vertical axis of the figure indicates the frequency of the component carrier, the horizontal axis indicates time, and each slot has a 0.5 - ms period. For example, a slot with a 20 - MHz bandwidth contains 1200 sub - carriers (SCs) with a 15 - kHz inter - carrier spacing. The frame includes DL slots, special slots, and UL slots. Each DL and UL slot has 7 respective single - carrier frequency - division multiple - access (SC - FDMA) symbols. Each symbol is indicated by an individual vertical column of the slot.

[0036] Figure 9 is a detailed view of the downlink slot of FIG. 8. The DL slot is used to transmit the physical downlink shared channel (PDSCH) that conveys payload traffic from the HU to the RU. Also, except for special slots, the DL slot includes the physical HARQ indicator channel (PHICH) that conveys HARQ ACK / NACK feedback to the RU. The physical downlink control channel (PDCCH) is also transmitted in this slot. The PDCCH provides the RU with PHY control information for the MCS and MIMO configuration for each RU that is dynamically scheduled in such a slot. Also, the PDCCH provides the RU with PHY control information for the MCS and MIMO configuration for each RU that is dynamically scheduled in one or more future UL slots.

[0037] To improve the latency for high-priority packets, 4 pairs of spectrum allocations at both ends of the system bandwidth can be assigned to different RUs, where the frequency gap between the two allocated chunks of a pair is the same between allocated pairs. The resource allocation is made in a semi-persistent scheduling (SPS) approach through dedicated messages from higher layers on the PDSCH channel. The size of each SPS allocation pair can be configured according to the expected traffic load pattern. For example, when there is no SPS allocation, no physical resource blocks (PRBs) are allocated for SPS transmission. When the expected traffic is larger, two (one on each side of the spectrum), or four (two on each side of the spectrum) PRBs can be allocated. Each RU can have any SPS allocation or multiple adjacent SPS allocations. In one embodiment, all four SPS allocation pairs are of the same size. Preferably, most of the remaining frequency-time resources in the slot are dynamically assigned to a single RU, excluding PS, PDCCH, PHICH, and SPS allocations, and the scheduling information for such RU is conveyed in the PBCH.

[0038] Similar to LTE, to minimize complexity, all allocation sizes are multiples of PRBs (12 sub-carriers) and are restricted to a defined set of sizes. The only exception is for SPS allocations where the closest number of sub-carriers can be made to the nominal target allocation size (2 or 4 PRBs). This minimizes the wasted guard band between SPS and PDSCH or PUSCH.

[0039] Figure 10 illustrates various DL slot formats for different component carriers (CCs). A significant improvement over LTE is that the dynamic allocation size of PDSCH varies between SC-FDMA symbols and is adjusted to fit within the control channel frequency multiplexed in the same symbol. A transport block carrying user data in a slot is mapped to consecutive SC-FDMA data symbols of the slot. This is different from LTE in that the mapping is done between SC-FDMA symbols of different sizes. This advantageously maximizes the utilization of all remaining resource elements and improves spectral efficiency. In a system with a primary CC of 10, 15, or 20 MHz, the SPS allocation starts from the second SC-FDMA symbol in a slot. In a system with a primary CC of 5 MHz, the SPS allocation starts from the third SC-FDMA symbol in a slot. The SPS allocation is applied only to the primary CC and there is no SPS allocation assigned in the secondary CC. Other than this difference, the DL slot has the same format for both the primary and secondary CCs.

[0040] Figure 11 is a diagram of various special slot formats for different component carriers (CCs) and system bandwidths. The RU is UL synchronized to the HU. As a result, a guard time is required for each DL·UL transition. The frame structure re-uses for that purpose the special sub-frame concept of the TD-LTE frame adapted to special slots. The special slot includes DwPTS in SC-FDMA symbols 0 to 3, a guard period (GP) in SC-FDMA symbol 4, and UpPTS in SC-FDMA symbols 5 to 6. As described above, the DwPTS and UpPTS of the NLOS special slot occur simultaneously with the DwPTS and UpPTS transmissions of the TD-LTE special sub-frame, thereby preventing the transmitter of one system from interfering with the receiver of another co-located system. UpPTS is for the transmission of short physical random access channels (PRACH) and sounding reference signals (SRS) from the RU. The PRACH channel can occur for each other special slot, can have a lower density such as 0.1 or 0.01, and can be based on the system frame number. Information about the PRACH configuration is broadcast via the PBCH. The PRACH is used in the HU for measurements for initial timing adjustment during the initial link setup procedure. The SRS is used for CSI estimation and timing offset estimation. The PHY information (MCS and MTMO configuration) for DwPTS is conveyed in the PDCCH of the previous DL slot. As a result, the PDCCH is not required in the special slot. Also, for simplicity, the special slot does not include any SPS allocation. SC-FDMA symbol 0 of DwPTS is a pilot signal (PS) frequency multiplexed with the synchronization signal (SS) in the primary CC. There is no SS in the secondary CC. SC-FDMA symbols 1 to 3 carry the physical broadcast channel (PBCH) and also, when the system bandwidth is larger than 5 MHz, the PDSCH. The PBCH provides the RU with system information and RU slot allocation information for the next frame for all CCs. The PBCH occupies the central 300 sub-carriers and is multiplexed in FDMA with the PDSCH. The PBCH is transmitted only on the primary CC.As a result, on the secondary CC, all of SC-FDMA symbols 1 to 3 are used to carry the PDSCH. The SC-FDMA symbol 0 in the primary CC carries a synchronization signal (SS) for cell search / detection and initial synchronization of the primary CC. The SS is assigned the same tones as the PBCH and is frequency multiplexed with the PS in SC-FDMA symbol 0.

[0041] Figure 12 is a diagram of various UL slot formats for different component carriers (CCs). The UL slot is used to transmit a physical uplink shared channel (PUSCH) that conveys payload traffic from the RU to the HU. The SC-FDMA symbol 0 of the PUSCH is a pilot symbol (PS). A physical uplink control channel (PUCCH) is also transmitted in this slot only in the primary CC. The PUCCH carries HARQ ACK / NACK feedback, channel quality indicator (CQI), rank indicator (RI), and scheduling request (SR) from the RU for all CCs. The PUCCH occupies both ends of the slot bandwidth and is multiplexed in FDMA with the PUSCH. The PUCCH occupies a maximum of 8 PRBs. Similar to the DL slot, SPS allocation is also used in the UL slot of the primary CC. A pair of spectrum allocations at both ends of the system bandwidth can be assigned to each RU in each UL slot. The resource allocation is made in a semi-persistent scheduling (SPS) approach. Most of the remaining frequency-time resources in the slot (excluding PS, PUCCH, and SPS allocation) are dynamically assigned to a single RU in a TDMA manner, and the scheduling information is conveyed in the PBCH.

[0042] FIG. 13 is a block diagram illustrating physical downlink shared channel (PDSCH) generation for an exemplary wireless system with a single transmit antenna. On the PDSCH, for each stream per transmission time interval (TTI) and in a 2×2 multiple-input multiple-output (MIMO) system where 2 data streams can be transmitted, one transport block is transmitted and two transport blocks are transmitted in parallel. A 24-bit cyclic redundancy check (CRC) 1300 is added onto each transport block using LTE's CRC-24A. The cyclic redundancy check (CRC) is not added to the forward error correction (FEC) block (turbo + RS). There is no turbo code CRC. The initial termination is not a condition in turbo decoding. One CRC-added transport block corresponds to an integer number of forward error correction (FEC) blocks, where FEC means concatenated turbo and Reed-Solomon (RS) codes. Also, in one FEC block, there are an integer number of turbo blocks and an integer number of Reed-Solomon (RS) blocks 1302. For example, one transport block after CRC can be mapped to 2 FEC blocks, and each FEC block can have 3 turbo blocks and 6 RS blocks. The CRC-added transport block is encoded by an RS encoder such as RS(255, 255 - 2T), where T is the error correction capability in bytes of the RS code. Typically, a shortened RS code with form RS(255 - S, 255 - 2T - S) is used. For example, RS(192, 184) and RS(128, 122) can be used. Also, in short allocations such as semi-persistent scheduling (SPS) allocation, RS code shortening is used as an additional rate matching (RM) scheme on top of turbo code block rate matching. The RS output block corresponding to one FEC block passes through a byte interleaver 1304. The interleaved byte symbols are used as input to a turbo encoder 1306. Then, turbo coding such as LTE's turbo code and LTE's RM is applied.

[0043] Bit-level scrambling 1308 is applied to the FEC-encoded bit stream. In a given RU, different codes may be applied to consecutive FEC blocks and transport blocks of different layers in the same allocation, but the same code set repeats over a TTI, and cell-specific code hopping is applied between FEC blocks and codewords over a slot. This provides the advantage of enabling a simple implementation where all codes are pre-computed, stored in memory, and reused for each TTI.

[0044] In each FEC block k in codeword q, the bits The block of JPEG2025111643000002.jpg1168 is scrambled before modulation, and according to JPEG2025111643000003.jpg1291, becomes the scrambled bits of the block of JPEG2025111643000004.jpg1172. Here, JPEG2025111643000005.jpg917 is the number of bits in FEC block k of codeword q transmitted on the PDSCH. Here, the scrambling sequence c(q,k)(i) is preferably a Gold sequence, as is known in the art.

[0045] The scrambling sequence generator is initialized at the start of each FEC block, with JPEG2025111643000006.jpg9103, where JPEG2025111643000007.jpg840 is the RU index in the cell, and JPEG2025111643000008.jpg811 is the physical layer cell identity. k’ and q’ are the hopping FEC block and codeword indices given by JPEG2025111643000009.jpg2490. Here, n(mod m) means n modulo m, JPEG2025111643000010.jpg1371 is the FEC block index, JPEG2025111643000011.jpg1134 is the number of FEC blocks in the transport block associated with codeword q in the case of RU s in slot n nRU and is the number of FEC blocks in the transport block associated with codeword q in the case of RU JPEG2025111643000012.jpg1028 is the number of codewords in the case of RU s in slot n nRU and is the number of codewords in the case of RU ·n s is the slot index in the frame, ·At most two codewords can be transmitted in one slot, that is, JPEG2025111643000013.jpg1122. In the case of single codeword transmission, q = 0.

[0046] After bit-level scrambling 1308, the data stream is symbol mapped 1310 and applied to the serial-parallel converter 1312. The parallel symbols are converted to frequency-domain symbols by DFT 1314, and subcarriers are mapped 1316. The mapped subcarriers are then converted to the time domain by IFFT 1318 and applied to the parallel-serial converter 1320. A cyclic prefix 1322 is added to the resulting data stream, and a half-carrier frequency offset 1324 is applied.

[0047] FIG. 14 is a block diagram illustrating physical downlink control channel (PDCCH) generation for an exemplary wireless system with two transmit antennas. Since PDCCH generation is functionally similar to the above-described PDSCH generation, only different blocks will be described hereinafter. The PDCCH is used to transmit downlink control information (DCI). The PDCCH is link-based, and thus each dynamic slot resource has its own PDCCH DCI, and each RU needs to search for PHY information in the PDCCH DCI that is assigned by the PBCH to properly decode its downlink PHY channel and properly transmit its uplink PHY channel. In particular, the PDCCH in each DL slot carries PHY control information (MCS and MTMO configuration) for the RUs dynamically scheduled in that slot. The PDCCH also carries PHY control information (MCS and MTMO configuration) for the RUs dynamically scheduled in one or more future UL slots. Finally, the PDCCH indicates potential assignment pre-emptions by HARQ retransmission for both dynamic and SPS assignments.

[0048] A 16-bit CRC is first added to the DCI bits, which then pass through an RS encoder with a mother code RS (KRS = 255, NRS = 247) that uses code shortening to adapt to a small input payload. Each such RS block has tail biting of LTE (R = 1 / 3, Κ = 7) with rate matching ( tForm an FEC block that feeds convolutional encoding 1400. This PDCCH MCS is selected such that the required signal-to-noise ratio (SNR) for PDCCH detection at FER = 1% is 3 dB lower than that for a lower MCS of PDSCH and PUSCH, so that PDCCH information is carried over to the RU in the worst-case scenario. The encoded bits are channel interleaved and scrambled 1402 before they are mapped to modulation symbols. QPSK is a preferred modulation format because of its robustness in a noisy channel. In the case of 2 transmit antennas or cross-polarization, the PDCCH is transmitted in a rank 1 transmission with an Alamouti type of space-frequency block code (SFBC) 1404.

[0049] Each RU uses DL synchronization signals (SS) and pilot signals (PS) for signal and boundary detection, initial carrier frequency offset (CFO) estimation, initial symbol timing and tracking, and channel estimation. The PS sequence is generated in the same way as in LTE. Only one base sequence is available for each base sequence group so that a total of 30 base sequences are available regardless of the sequence length. Group hopping is not applied. The same base sequence is used for both UL and DL. The base sequence index used in the cell for PUSCH / PDSCH C / RPS JPEG2025111643000014.jpg1354 is broadcast in the PBCH. The same base sequence is used for both PUCCH and SRS, and this index JPEG2025111643000015.jpg1355 is provided individually to each RU by the HU via higher layer dedicated signaling in the RAR.

[0050] Within the scope of the claims of the present invention, modifications can be made to the illustrated embodiments described, and other embodiments are possible. The embodiments can be implemented in software, hardware, or a combination of both.

Claims

1. A method for operating a wireless communication system, comprising: communicating with a first wireless transceiver using a first data frame having a first transmission time interval; and communicating with a second wireless transceiver using a second data frame having a second transmission time interval different from the first transmission time interval. A method as described above.

2. The method according to claim 1, further comprising: transmitting data between the first data frame and the second data frame.

3. The method according to claim 1, wherein: the period of the second transmission time interval is an integer multiple of the period of the first transmission time interval.

4. The method according to claim 1, wherein: the period of the second frame is an integer multiple of the period of the first frame.

5. The method according to claim 1, wherein: the first data frame includes a plurality of slots, each slot having the first transmission time interval, and a first symbol at the time of each slot of the plurality of slots includes a pilot signal.

6. The method according to claim 1, wherein: the first data frame includes a plurality of slots, each slot having the first transmission time interval and having a plurality of respective symbols, and a transport block having data for a single user is mapped to consecutive symbols in a certain slot of the plurality of slots.

7. The method according to claim 6, wherein: the consecutive symbols include different respective allocation sizes.

8. The method according to claim 1, wherein: the first data frame includes a plurality of slots, each slot having the first transmission time interval and having a plurality of respective symbols, a first portion of each symbol is a semi-persistent allocation, and a second portion of each symbol is a dynamic allocation.

9. The method according to claim 8, wherein: the semi-persistent allocation is communicated via a dedicated message in a physical data shared channel (PDSCH).

10. The method according to claim 1, further comprising: communicating with the first wireless transceiver at a first time using the first data frame; and In synchronization with the first data frame, communicating with the second wireless transceiver at the first time by a third data frame having the second transmission time interval. A method comprising the above. **Claim 11** The method according to claim 10, wherein the step of communicating by the first data frame is one of an uplink and a downlink, and the step of communicating with the second wireless transceiver in synchronization with the first data frame is the one of the uplink and the downlink. **Claim 12** The method according to claim 10, wherein the first and third data frames use the same frequency resource. **Claim 13** A method of communicating within a wireless bandwidth, communicating with a first wireless transceiver by a first data frame having a first transmission time interval at a first time using a first frequency resource of the wireless bandwidth by one of an uplink and a downlink, and communicating with a second wireless transceiver by a second data frame having a second transmission time interval at the first time using a second frequency resource of the wireless bandwidth by the one of the uplink and the downlink. A method comprising the above. **Claim 14** A method of operating a wireless communication system, communicating with a second wireless transceiver by a first wireless transceiver by a first data frame having a first transmission time interval by one of an uplink and a downlink, including wherein the first data frame communicates data with a third wireless transceiver by one of an uplink and a downlink by a second data frame having a second transmission time interval different from the first transmission time interval, and the first and second data frames use the same carrier frequency. **Claim 15** The method according to claim 14, wherein the period of the second transmission time interval is an integer multiple of the period of the first transmission time interval. **Claim 16** The method according to claim 14, wherein the period of the second frame is an integer multiple of the period of the first frame. **Claim 17** The method according to claim 14, A method, wherein the first data frame includes a plurality of slots, each slot has the first transmission time interval, and a first symbol at the time of each slot of the plurality of slots includes a pilot signal.

18. The method according to claim 14, wherein the first data frame includes a plurality of slots, each slot has the first transmission time interval, and has a plurality of symbols respectively, and a transport block having data for a single user is mapped to consecutive symbols of a certain slot of the plurality of slots.

19. The method according to claim 14, a step of communicating with the second wireless transceiver at a first time by the first data frame, and a step of communicating with the third wireless transceiver at the first time by the third data frame having the second transmission time interval by one of the uplink and the downlink. A method comprising the above.

20. The method according to claim 19, wherein the step of communicating by the first data frame is synchronized with the step of communicating by the third data frame.

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