Extended communication coverage system for short random access channel format

Abstract

A communication system having an extended communication coverage system for short random access channel (RACH) format is provided that includes a base station. The base station is configured to interface communications between a core network of a service provider and a distributed antenna system. The base station is configured to generate a full length N symbol RACH preamble sequence signal that is transmitted by a plurality of RAUs of the DAS. A full N symbol cross-correlation between a returned signal and the generated signal is conducted by the base station and a delay is determined based on a maximum peak magnitude in a result of the full N symbol cross-correlation. A timing advance associated with the delay is sent to a user equipment (UE) seeking to communicate with the core network to allow the UE to synchronize communications.

Description

EXTENDED COMMUNICATION COVERAGE SYSTEM FOR SHORT RANDOM ACCESS CHANNEL FORMATCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This Application claims priority to U.S. Provisional Application Serial No. 63 / 581,895, same title herewith, filed on September 11, 2023, which is incorporated in its entirety herein by reference.BACKGROUND

[0002] Wireless cellular service providers use base stations to implement wireless communication links with user equipment, such as mobile phones. In particular, a base station is typically in communication with one or more antennas that receive and transmit radio frequency signals to and from user equipment. Each base station in turn is in communication with a core network of a service provider. The coverage area of a base station is limited by the transmit power of the associated signals. Moreover, the coverage provided by the transmitted signals is influenced by many other factors such as physical obstacles and interference. Hence, wireless coverage in buildings and stadiums has been traditionally poor when served only from conventional “macro” base stations. One way that a wireless cellular service provider can improve the coverage provided by a given base station or group of base stations is by using a distributed antenna system (DAS).

[0003] To increase throughput, a base station may share a communication channel among wireless devices. For example, a random-access channel (RACH) may be shared among wireless devices. Switched Ethernet may be used to control the passing of information between the base station and the antennas. In a system that implements RACH, when user equipment (UE) wants to make a mobile originating call, the UE schedules its use of the RACH. The UE connects to a cellular network by using a RACH procedure which includes listening to a broadcast channel that provides synchronization information, implementing synchronization to the cellular network, and configuring itself for the collection of RACH preambles and RACH opportunities supported by the base station. Once synchronization occurs, the UE picks a preamble at random and then tries to access the RACH by transmittingthe preamble. The base station in this system listens at every UL RACH opportunity to see if any UEs are transmitting a preamble.

[0004] For the communication system to provide a desired quality of service (QoS), latencies encountered as signals are communicated between bases stations and user UEs must be effectively dealt with within the system. When a wireless base station (gNB) uses a single UL Ethernet frame boundary for RACH and other channels (e.g., physical uplink shared channel (PUSCH)), any latency between the base station and the access point (AP) / remote unit (RU) antennas must be accounted for when selecting a zero-correlation zone (ZCZ) configuration and corresponding time Tcsbetween RACH cyclic shifts (preambles). The roundtrip latency plus the roundtrip over-the-air (OTA) latency must not exceed Tcsin order to have reliable RACH performance with accurate determination of the UE’s preamble selection. The requirement for Tcsis thus relatively large when latency is relatively large, requiring a relatively large number of root-sequences per RACH opportunity.Implementation complexity increases and RACH performance generally degrades, as the number of root-sequences increases. Furthermore, fiber reach to the RU (which contributes to latency) is limited, depending on the resolution available with Tcsand the ZCZ configuration options.

[0005] With 5G short RACH formats, a base preamble length is the same as the PUSCH symbol length (e.g., ~36us for 30kHz numerology), and transmission of the base preamble is repeated in N consecutive symbols. For a UE to successfully connect to a cell using RACH, the roundtrip latency from the base station to the UE, including any DAS delay, must be no more than the configured time between RACH cyclic shifts. Hence, to maximize system latency tolerance and cell / fiber reach the base station configures only a single cyclic shift for RACH.

[0006] Upon detection in RACH, the base station issues a timing advance (TA) directive to the UE based on the delay it measures for the RACH reception. Delay can be estimated based on cross correlation of a base preamble with the reception in the RACH interval. In view of the repetitions used with short RACH formats, a conventional base station performs the cross correlation in a computationally efficiently manner by first coherently summing the N receptions for the preamble repetitions, before performing the cross-correlation with the base preamble, typically by performing the IFFT of the product of the FFT of the summed receptions times the conjugate of the FFT of the base preamble.

[0007] With the computationally efficient approach for estimating delay in RACH, the delay can only be a measured modulo symbol length. If the roundtrip latency between the base station and UE exceeds the symbol length, the delay estimate wraps around zero, and the TA directive will not match the actual TA needed for the UE. A consequence of a roundtrip latency exceeding the symbol length is that UL performance will be degraded. For 30 kHz numerology, the permissible roundtrip latency is limited to approximately 36ps.

[0008] For the reasons stated above and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for effectively and efficiently estimating the delay in RACH beyond a symbol length without UL performance degradation.SUMMARY

[0009] The following summary is made by way of example and not by way of limitation. It is merely provided to aid the reader in understanding some of the aspects of the subject matter described. Embodiments provide a system that measures accurately the roundtrip latency by estimating RACH delays by cross-correlation of a full N-symbol repeated RACH preamble.

[0010] In one embodiment, a communication system having extended communication coverage using a short random access channel format is provided. The communication system includes a base station. The base station is configured to interface communications between a core network of a service provider and a distributed antenna system (DAS), where the DAS provides a cellular coverage area for user equipment (UE) with a plurality remote antenna units (RAUs). The base station is configured to generate a full length N symbol random access channel (RACH) preamble sequence of repeated RACH base preambles, each RACH base preamble having a length one symbol; apply a full length N symbol crosscorrelation on a received signal from a UE seeking to communicate with the core network through the DAS on the RACH by transmitting a full length N symbol RACH preamble sequence, wherein an output sample in the applied full length N symbol cross-correlation is obtained with multiply-adds using samples in all N symbols of the generated full length N symbol random access channel (RACH) preamble sequence, further wherein the crosscorrelation result has a length greater than one symbol; determine a maximum peak magnitude in the cross-correlation; identify a delay corresponding to the determinedmaximum peak magnitude; and provide a timing advance associated with the delay to the UE seeking to communicate with the core network to allow the UE seeking to communication with the core network to synchronize communications.

[0011] In another embodiment, a communication system having an extended communication coverage system for short random access channel format is provided. The communication system includes a distributed antenna system (DAS) and a base station. The DAS including a plurality of remote antenna units (RAUs) and a master unit (MU). The RAUs are configured to communicate wirelessly with user equipment via radio frequency (RF) signals. The master unit (MU) is in communication with the plurality of RAUs. The MU is configured to generate one or more downlink transport signals that are communicated to at least one RAU of the plurality of RAUs and received uplink transport signals from at least one RAU of the plurality of RAUs. The base station includes at least one radio unit (RU). The at least one RU is in communication with the MU. The at least one RU is configured to implement physical layer functions and provide an RF interface. The at least one RU is further configured to generate a full length N symbol random access channel (RACH) preamble sequence of repeated RACH base preambles, each RACH base preamble having a length one symbol; apply a full length N symbol cross-correlation on a received signal from a UE seeking to communicate with the core network through the DAS on the RACH by transmitting a full length N symbol RACH preamble sequence, wherein an output sample in the applied full length N symbol cross-correlation is obtained with multiply-adds using samples in all N symbols of the generated full length N symbol random access channel (RACH) preamble sequence, further wherein the cross-correlation result has a length greater than one symbol; determine a maximum peak magnitude in the cross-correlation; identify a delay corresponding to the determined maximum peak magnitude; and provide a timing advance associated with the delay to the UE seeking to communicate with the DAS.

[0012] In yet another embodiment, a method of operating a communication system having an extended communication coverage system for short random access channel format is provided. The method includes transmitting a full length N symbol RACH preamble sequence to a remote location, the preamble sequence including a plurality of base preambles, each base preamble having length one symbol; receiving an uplink signal (UL) from a user equipment (UE) at a remote location seeking to communicate over the RACH that includes a full length N symbol RACH preamble sequence; applying a full length N symbol cross-correlation on the received UL signal from the UE, wherein an output sample in the applied full length N symbol cross-correlation is obtained with multiply-adds using samples in all N symbols of the generated full length N symbol random access channel (RACH) preamble sequence, further wherein the cross-correlation result has a length greater than one symbol; determining a maximum peak magnitude in the full length symbol cross-correlation; identifying a delay corresponding to the determined maximum peak magnitude; and providing a timing advance associated with the delay to the UE to allow synchronization of the communication system.BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The present invention can be more easily understood and further advantages and uses thereof will be more readily apparent, when considered in view of the detailed description and the following figures in which:

[0014] Figure l is a block diagram illustrating one exemplary embodiment of a radio access network communication system in which a roundtrip latency can be measured accurately and effectively with cross-correlation of a full N-symbol length RACH according to an example aspect of the preset invention.

[0015] Figure 2A is a magnitude verses time graph of a transmitted short preamble with repetitions of a base preamble according to an example aspect of the preset invention.

[0016] Figure 2B is a magnitude verses time graph of a received short preamble with repetitions of the base preamble that are delayed according to an example aspect of the preset invention.

[0017] Figure 2C is a magnitude verses time graph of a cross-correlation of the generated and trip delayed short preamble with repetitions of a base preamble of Figures 2A and 2B respectfully.

[0018] Figure 3 illustrates a flow diagram of a method of creating an extended communication coverage system for short RACH format according to an example aspect of the preset invention.

[0019] In accordance with common practice, the various described features are not drawn to scale but are drawn to emphasize specific features relevant to the present invention. Reference characters denote like elements throughout Figures and text.DETAILED DESCRIPTION

[0020] In the following detailed description, reference is made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration specific embodiments in which the inventions may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that changes may be made without departing from the spirit and scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the claims and equivalents thereof.

[0021] Embodiments of the present invention provide an extended coverage system for short random access channel (RACH) formats. Embodiments provide a system that measures accurately the roundtrip latency by estimating RACH delays using a cross-correlation of a full length N-symbol RACH preamble sequence where N is the number of symbols (each symbol makes up a base preamble) in the RACH preamble sequence. The full crosscorrelation produces 2N-1 peaks in general, but the pertinent peak is identified as the one with maximum magnitude, and the delay for this peak represents the actual roundtrip latency. After the bases station issues a TA directive to the UE corresponding to the actual delay, the UE connects without degradation of UL performance.

[0022] Figure l is a block diagram illustrating one exemplary embodiment of a radio access network (RAN) communication system 100 in which the roundtrip latency can be measured accurately and effectively with cross-correlation of a full N-symbol length RACH preamble sequence.

[0023] The communication system 100 shown in Figure 1 implements at least one base station entity 102 to serve a cell. Each such base station entity 102 can also be referred to here as a “base station” or “base station system” (and, which in the context of a fourth generation (4G) Long Term Evolution (LTE) system, may also be referred to as an “evolved NodeB”, “eNodeB”, or “eNB” and, in the context of a fifth generation (5G) New Radio (NR) system, may also be referred to as a “gNodeB” or “gNB”).

[0024] In general, each base station 102 is configured to provide wireless service (cellular coverage area) to various items of user equipment (UEs) 150 served by an associated cell in a remote location. Unless explicitly stated to the contrary, references to Layer 1, Layer 2, Layer 3, and other or equivalent layers (such as the Physical Layer or the Media AccessControl (MAC) Layer) refer to layers of the particular wireless interface (for example, 4G LTE or 5G NR) used for wirelessly communicating with UEs 150. Furthermore, it is also to be understood that 5G NR embodiments can be used in both standalone and non- standalone modes (or other modes developed in the future) and the following description is not intended to be limited to any particular mode. Moreover, although some embodiments are described here as being implemented for use with 5GNR, other embodiments can be implemented for use with other wireless interfaces and the following description is not intended to be limited to any particular wireless interface.

[0025] In the specific exemplary embodiment shown in Figure 1, each base station 102 is implemented as a respective 5G NR gNB 102 (only one of which is shown in Figure 1 for ease of illustration). In this embodiment, each gNB 102 is partitioned into one or more central unit entities (CUs) 108, one or more distributed unit entities (DUs) 110, and one or more radio units (RUs) 109. In such a configuration, each CU 108 implements Layer 3 and non-time critical Layer 2 functions for the gNB 102. In the embodiment shown in Figure 1, each CU 108 is further partitioned into one or more control-plane entities 114 and one or more user-plane entities 116 that handle the control-plane and user-plane processing of the CU 108, respectively. Each such control-plane CU entity 114 is also referred to as a “UUCP” 114, and each such user-plane CU entity 116 is also referred to as a "CU-UP" 116. Also, in such a configuration, each DU 110 is configured to implement the time critical Layer 2 functions and, except as described below, at least some of the Layer 1 functions for the gNB 102. In this example, each RU 109 is configured to implement the physical layer functions for the gNB 102 that are not implemented in the DU 110 as well as the RF interface. Also, each RU 109 includes a plurality of antenna ports 111

[0026] Each RU 109 is communicatively coupled to the DU 110 serving it (for example, using a switched Ethernet network, in which case each RU 109 and each physical node on which each DU 110 is implemented includes one or more Ethernet network interfaces to couple each RU 109 and each DU physical node to the switched Ethernet network in order to facilitate communications between the DU 110 and the RUs 109). In one implementation, a fronthaul interface promulgated by the O-RAN alliance is used for communication between the DU 110 and the RUs 109. In another implementation, a proprietary fronthaul interface that uses a so-called “functional split 7-2” for at least some of the physical channels (forexample, for the PDSCH and PUSCH) and a different functional split for at last some of the other physical channels (for example, using a functional split 6 for the PRACH and SRS).

[0027] In such an example, each CU 108 is configured to communicate with a core network 122 of the associated wireless operator using an appropriate backhaul network 124 (typically, a public wide area network such as the Internet).

[0028] Although Figure 1 (and the description set forth below more generally) is described in the context of a 5G embodiment in which each logical base station entity 102 is partitioned into a CU 108, DUs 110, and RUs 109 and, for at least some of the physical channels, some physical -lay er processing is performed in the DUs 110 with the remaining physical -lay er processing being performed in the RUs 109, it is to be understood that the techniques described here can be used with other wireless interfaces (for example, 4G LTE) and with other ways of implementing a base station entity (for example, using a conventional baseband band unit (BBU) / remote radio head (RRH) architecture). Accordingly, references to a CU, DU, or RU in this description and associated figures can also be considered to refer more generally to any entity (including, for example, any “base station” or “RAN” entity) implementing any of the functions or features described here as being implemented by a CU, DU, or RU.

[0029] Each CU 108, DU 110, and RU 109, and any of the specific features described here as being implemented thereby, can be implemented in hardware, software, or combinations of hardware and software, and the various implementations (whether hardware, software, or combinations of hardware and software) can also be referred to generally as “circuitry,” a “circuit,” or “circuits” that is or are configured to implement at least some of the associated functionality. When implemented in software, such software can be implemented in software or firmware executing on one or more suitable programmable processors (or other programmable device) or configuring a programmable device (for example, processors or devices included in or used to implement special-purpose hardware, general-purpose hardware, and / or a virtual platform). In such a software example, the software can comprise program instructions that are stored (or otherwise embodied) on or in an appropriate non-transitory storage medium or media (such as flash or other non-volatile memory, magnetic disc drives, and / or optical disc drives) from which at least a portion of the program instructions are read by the programmable processor or device for execution thereby (and / or for otherwise configuring such processor or device) in order for the processor ordevice to perform one or more functions described here as being implemented the software. Such hardware or software (or portions thereof) can be implemented in other ways (for example, in an application specific integrated circuit (ASIC), etc.).

[0030] Moreover, each CU 108, DU 110, and RU 109, can be implemented as a physical network function (PNF) (for example, using dedicated physical programmable devices and other circuitry) and / or a virtual network function (VNF) (for example, using one or more general purpose servers (possibly with hardware acceleration) in a scalable cloud environment and in different locations within an operator’s network (for example, in the operator’s “edge cloud” or “central cloud”). Each VNF can be implemented using hardware virtualization, operating system virtualization (also referred to as containerization), and application virtualization as well as various combinations of two or more the preceding. Where containerization is used to implement a VNF, it may also be referred to as a “containerized network function” (CNF).

[0031] For example, in the exemplary embodiment shown in Figure 1, each RU 109 is implemented as a PNF and is deployed in or near a physical location where radio coverage is to be provided and each CU 108 and DU 110 is implemented using a respective set of one or more VNFs deployed in a distributed manner within one or more clouds (for example, within an “edge” cloud or “central” cloud).

[0032] Each CU 108, DU 110, and RU 109, and any of the specific features described here as being implemented thereby, can be implemented in other ways. In the exemplary embodiment shown in Figure 1, each base station 102 is coupled to a distributed antenna system (DAS) 130 in order to improve the wireless coverage provided by the base station 102.

[0033] In the exemplary embodiment shown in Figure 1, each base station 102 is coupled to a distributed antenna system (DAS) 130 in order to improve the wireless coverage provided by the base station 102. More specifically, in the exemplary embodiment shown in Figure 1, an RU 109 of each base station 102 is coupled to the DAS 130 using an analog RF interface. More specifically, the DAS 130 is coupled to the set of antenna ports 111 of the RU 109 that would otherwise be used to couple the RU 109 to a set of antennas. The connection between the base station 102 and the DAS 130, in this example, may occur using one or more coaxial cables and possibly some intermediary attenuators or a point-of-interface(POI) type device connecting the antenna ports 111 of the RU 109 to antenna ports 132 of a master unit (MU) 135 of the DAS 130

[0034] In an example DAS 130, radio frequency (RF) signals may be transported between a master unit 135 and one or more RAU 140 using one or more transport cables 136, that are part of the fronthaul of the communication system 100. The transport cables 136 may be part of a fiber distribution network.

[0035] Traditionally, RF signals transmitted from the base stations 102 (also referred to here as "downlink RF signals") are received at the master unit 135. The master unit 135 uses the downlink RF signals to generate one or more downlink transport signals that are distributed to one or more of the RAUs 140 over the transport cables 136. Each such RAU 140 receives a downlink transport signal and generates a version of the downlink RF signals based on the downlink transport signal and causes the generated downlink RF signals to be radiated from at least one antenna 144 coupled to or included in that RAU 140.

[0036] A similar process is performed in the uplink direction. RF signals transmitted are from user equipment 150 (also referred to here as "uplink RF signals"). Each such uplink RF signal is intended for a base station 102 coupled to the master unit 135. Each RAU 140 receives uplink RF signals transmitted from user equipment 150 within its associated coverage area. Each RAU 140 uses the received uplink RF signals to generate an uplink transport signal that is transmitted from the RAU 140 to the master unit 135. The MU 135 receives uplink transport signals from the various RAUs 140 coupled to it. An extension unit (EU) 138 may be used between the MU 135 and one or more RAU 140 to extend the coverage of the DAS 130.

[0037] For each base station 102 coupled to the master unit 135, the master unit 135 ultimately generates uplink RF signals from the combined uplink signals for that base station 102, which are provided to that base station 102. Each RAU 140 can be coupled to each master unit 135 either directly or indirectly via one or more intermediate devices (such as another RAU 140 or an expansion unit (EU) 138). In this way, the coverage of each base station 102 can be expanded using the DAS 130. In one example, a master unit 135 of the DAS 130 is in communication with (or coupled to) the antenna ports 111 of the RUs 109 as discussed above.

[0038] Although in the exemplary embodiment shown in Figure 1 each base station 102 is coupled to a DAS 130, it is to be understood that the techniques described below can beused with a base station 102 that is not connected to a DAS 130. For example, the techniques described below can also be a base station 102 that is not connected to a DAS 130 but is implemented using a so-called “non-ideal” fronthaul network. As used here, a “non-ideal” fronthaul network is one that may not always be able to satisfy the minimum bandwidth and / or latency requirements for the base station 102 that would otherwise be necessary if the techniques described below were not used.

[0039] As discussed above, example embodiments of the base station 102 may use Ethernet switching in communications between service provider’s core network 122 and the UEs 150 through the extended distribution network provided by the DAS 130. The use of Ethernet switching adds latency due to the handling of the Ethernet frames that includes reconceiving the Ethernet frame, buffering the Ethernet frame and forwarding the Ethernet frame.

[0040] As described above, specific features described here as being implemented thereby, can be implemented in hardware, software, or combinations of hardware and software. In one example the circuitry of the DU 110 described above provides specific functions including control of the Ethernet switching function and frame boundaries as discussed in detail below. Such functions may include the functions of processing RACH independently from PUSCH and other channels to reduce latency while maintaining QoS and implementing the Ethernet switching. The circuitry of the DU 110 of the base station 102 is further configured to detection communication signals in the RACH, PUSCH and other communication channels.

[0041] Further as discussed above, latency in the communication system 100 has implications. The first implication relates to RACH performance. The DU 110 processes short RACH formats in a computationally efficient manner by coherently summing over end repetitions. A delay includes only one cyclic shift, so the delay is computed by correlating a summed reception against a space transmit preamble that is sent in one symbol.

[0042] Latency may be determined in a computationally efficient manner by just summing together the N-symbols and multiplying by a fast Fourier transform (FFT) of the base preamble sequence. The result will be a single impulse, or single peak which corresponds to whatever delay was in the round trip from base station 102 back around to base station 102 by way of the RAU 140 and the UE 150. The latency includes over the air latency and latency in the DAS latency in the DAS 130. If the round-trip latency is beyond36 microseconds, which corresponds to the length of a symbol, the single peak will be located beyond the symbol boundary which will cause an issue when another UE 150 tries to use the RACH.

[0043] In embodiments, instead of conducting the computationally efficient crosscorrelation based on one symbol, a cross-correlation across a full length N-symbol length RACH sequence (a repeated RACH base preamble) is computed. This allows for an accurate determination of round-trip latency without limitation. Although this process, it is significantly less computationally efficient than the previous ended processing for the DU 110, it allows for the determination of an extended DAS round trip delay that may include fiber links latency in the DAS 130 as well as over the air latency.

[0044] Referring to Figure 2 A, an example of a transmitted magnitude verses time graph200 with a short preamble with four repetitions of a base preamble is provided separates by symbol boundaries 202. This is, in this example, a select number N of repeated length symbols (repeated base preambles) equals four. A base preamble, of this four-symbol repeated preamble sequence, includes a select number of samples which, in this example, equals 100 samples. A time lag in a received magnitude verses time graph 220 is illustrated in Figure 2B. The received preamble with delay is 175 samples in this example. Hence, the round-trip latency between the transmitted RACH preamble sequence (repeated base preambles) signal and a returned signal is 175 samples in this example.

[0045] As discussed above, in order to determine the round-trip latency, a crosscorrelation across a full symbol length RACH reception. Figure 2C illustrates a magnitude verse time graph 250 for a full N symbol length (4x100) RACH sequence cross-correlation as it relates to the time lag in the cross-correlation between the transmitted magnitude verses time graph 200 of Figure 2A and the received magnitude verses time graph 220 of Figure 2B. As a result of the cross-correlation, several peaks 252 occur in the cross-correlation magnitude verses time graph 250. However, only one maximum peak magnitude 254 occurs. The maximum peak magnitude 254 occurs at 175 samples which is the determined delay.

[0046] To a first approximation, the cross-correlation produces a base channel impulse response (IR). The delay is indicated by the largest magnitude in the base channel IR. This is the two-way delay accumulated in the downlink communication to the UE 150 and uplink direction back to the RU 109 in an example. The RACH preamble sequence consists of the N repeated symbols, so the cross-correlation consists of N-l attenuated replicas of the base IRon each side of the base IR. The further away a replica is from the base IR, the more attenuation it will have because fewer symbols are contributing signals to the crosscorrelation. So, the base IR (having a peak at the true-round-trip delay), may be identified as the replica having the maximum peak magnitude 254.

[0047] The maximum peak magnitude 254 provides the delay estimation that the RU 109, in an example performs to give a timing advance command to the UE 150. In another example, the determination of the maximum peak magnitude 254 may take place in another component of the base station, such as, but not limited to, DU 110.

[0048] Figure 3 illustrates a flow diagram 300 of a method of creating an extended communication coverage system for short RACH format. The flow diagram is provided as a series of sequential blocks. The sequence of blocks may occur in another order or even in parallel in other examples. Hence, the present invention is not limited to the sequence of blocks set out in Figure 3.

[0049] Flow diagram 300 starts at block 302 where a full length N symbol RACH preamble sequence is generated and broadcast. In an example, the RU 109 of the base station 102 generates a DL signal that includes the full length N symbol RACH preamble sequence. As described above, the full length N symbol RACH preamble sequence includes a select number of repeated RACH base preambles. Each RACH preamble has length one symbol. The remote antenna units 140 of the DAS 130 broadcasts the full length N symbol RACH preamble sequence in an example. As described above, the base RACH preamble has length one symbol. Hence, the number of length N symbols depends on the number of repeated RACH base preambles in the RACH preamble sequence. A UE 150, wanting to schedule the use of the RACH (seeking to communication with a core network 122 of a service provider), uses a RACH procedure that includes transmitting an UL signal back to the DAS 130 using the RACH that includes a repeated full length N symbol RACH preamble sequence at block 304.

[0050] The DAS 130 receives the UL signal from UE 150 at block 306. In one example, the RU 109 of the DAS 130 applies a full length N symbol cross-correlation on the received UL signal from the UE 150 seeking to communicate with the core network through the DAS on the RACH by transmitted a full length N symbol RACH preamble sequence at block 308. The applied full length N symbol cross-correlation is across all N symbols in the received UL signal. That is, in an example, an output sample in the applied full length N symbol cross-correlation is obtained with multiply-adds using samples in all N symbols of the generated full length N symbol random access channel (RACH) preamble sequence. The crosscorrelation result will have a length greater than one symbol. This is different than known methods that first sum N symbol receptions together and then perform a one symbol length cross-correlation.

[0051] From the results of the cross-correlation at block 308, a maximum peak magnitude 254 is determined at block 310. A corresponding delay to the maximum peak magnitude 254 is identified at block 312. A timing advance signal that is based on the delay is communicated to the UE 150 at block 314. The timing advance signal allows the latency to be delt with at the UE so that synchronization of the communication system can occur. The UE 150 is thereafter able to connect without degradation.EXAMPLE EMBODIMENTS

[0052] Example 1 includes a communication system having extended communication coverage using a short random access channel format. The communication system includes a base station. The base station is configured to interface communications between a core network of a service provider and a distributed antenna system (DAS), where the DAS provides a cellular coverage area for user equipment (UE) with a plurality remote antenna units (RAUs). The base station is configured to generate a full length N symbol random access channel (RACH) preamble sequence of repeated RACH base preambles, each RACH base preamble having a length one symbol; apply a full length N symbol cross-correlation on a received signal from a UE seeking to communicate with the core network through the DAS on the RACH by transmitting a full length N symbol RACH preamble sequence, wherein an output sample in the applied full length N symbol cross-correlation is obtained with multiply- adds using samples in all N symbols of the generated full length N symbol random access channel (RACH) preamble sequence, further wherein the cross-correlation result has a length greater than one symbol; determine a maximum peak magnitude in the cross-correlation; identify a delay corresponding to the determined maximum peak magnitude; and provide a timing advance associated with the delay to the UE seeking to communicate with the core network to allow the UE seeking to communication with the core network to synchronize communications.

[0053] Example 2 includes the communication system of Example 1, wherein the base station further includes at least one radio unit (RU) that is configured to implement physical layer functions. The at least one RU is further configured to identify the delay.

[0054] Example 3 includes the communication system of any of the Examples 1-2, wherein the base station further includes a distributed unit (DU) that is in communication with a master unit (MU) of the DAS. The DU is configured to implement time critical layer two functions and at least some of the layer one functions for the base station. The DU is further configured to identify the delay.

[0055] Example 4 includes the communication system of any of the Examples 1-3, wherein each symbol includes a plurality of samples.

[0056] Example 5 includes the communication system of any of the Examples 1-4, wherein the cross-correlation produces a base channel impulse response (IR), the delay being identified by a largest magnitude in the base channel IR.

[0057] Example 6 includes the communication system of any of the Examples 1-5, wherein the base station is configured to use ethernet switching in communications between the core network of the service provider and the UE through an extended distribution network provided by the DAS.

[0058] Example 7 includes the communication system of any of the Examples 1-6, wherein the base station further includes at least one at least one radio unit (RU) that is in communication with a master unit (MU) of the DAS. The at least one RU is configured to implement physical layer functions. The at least one RU is further configured to generate the full length N symbol random access channel (RACH) preamble sequence of repeated RACH base preambles; apply the full length N symbol cross-correlation on a received signal from a UE seeking to communicate with the core network through the DAS on the RACH by transmitting a full length N symbol RACH preamble sequence; determine the maximum peak magnitude in the cross-correlation, identify the delay corresponding to the determined maximum peak magnitude, and provide the timing advance associated with the delay to the UE seeking to communicate with the core network to allow the UE seeking to communication with the core network to synchronize communications. The communication system further including a distributed unit (DU) that is in communication with the at least one RU. The DU is configured to implement time critical layer two functions and at least some of the layer one functions for the base station. The at least one central unit (CU) is incommunication with the DU. The at least one CU is configured to implement layer three and non-time critical functions for the base station, the at least one CU further configured to communicate with the core network of the service provider using an appropriate backhaul network.

[0059] Example 8 includes the communication system of the Example 7, wherein the at least one RU includes a plurality of RU antenna ports that are communicatively coupled to MU antenna ports of the MU.

[0060] Example 9 includes a communication system having an extended communication coverage system for short random access channel format. The communication system includes a distributed antenna system (DAS) and a base station. The DAS including a plurality of remote antenna units (RAUs) and a master unit (MU). The RAUs are configured to communicate wirelessly with user equipment via radio frequency (RF) signals. The master unit (MU) is in communication with the plurality of RAUs. The MU is configured to generate one or more downlink transport signals that are communicated to at least one RAU of the plurality of RAUs and received uplink transport signals from at least one RAU of the plurality of RAUs. The base station includes at least one radio unit (RU). The at least one RU is in communication with the MU. The at least one RU is configured to implement physical layer functions and provide an RF interface. The at least one RU is further configured to, generate a full length N symbol random access channel (RACH) preamble sequence of repeated RACH base preambles, each RACH base preamble having a length one symbol; apply a full length N symbol cross-correlation on a received signal from a UE seeking to communicate with the core network through the DAS on the RACH by transmitting a full length N symbol RACH preamble sequence, wherein an output sample in the applied full length N symbol cross-correlation is obtained with multiply-adds using samples in all N symbols of the generated full length N symbol random access channel (RACH) preamble sequence, further wherein the cross-correlation result has a length greater than one symbol; determine a maximum peak magnitude in the cross-correlation; identify a delay corresponding to the determined maximum peak magnitude; and provide a timing advance associated with the delay to the UE seeking to communicate with the DAS.

[0061] Example 10 includes the communication system of Example 9, wherein each symbol includes a same number of samples.

[0062] Example 11 includes the communication system of any of the Examples 9-10, wherein the cross-correlation produces a base channel impulse response (IR). The delay being identified by a largest magnitude in the base channel IR.

[0063] Example 12 includes the communication system of any of the Examples 9-11, wherein the at least one RU includes a plurality of RU antenna ports that are communicatively coupled to MU antenna ports of the MU.

[0064] Example 13 includes the communication system of any of the Examples 9-12, wherein the base station is configured to use ethernet switching in communications between the core network of the service provider and the UE through an extended distribution network provided by the DAS.

[0065] Example 14 includes the communication system of any of the Examples 9-13, wherein the base station further includes a distributed unit (DU) and at least one central unit (CU). The DU is in communication with the at least one RU. The DU is configured to implement time critical layer two functions and at least some of the layer one functions for the base station. The at least one CU is in communication with the DU. The at least one CU is configured to implement layer three and non-time critical functions for the base station. The at least one CU is further configured to communicate with a core network of a service provider using an appropriate backhaul network.

[0066] Example 15 includes a method of operating a communication system having an extended communication coverage system for short random access channel format. The method includes transmitting a full length N symbol RACH preamble sequence to a remote location, the preamble sequence including a plurality of base preambles, each base preamble having length one symbol; receiving an uplink signal (UL) from a user equipment (UE) at a remote location seeking to communicate over the RACH that includes a full length N symbol RACH preamble sequence; applying a full length N symbol cross-correlation on the received UL signal from the UE, wherein an output sample in the applied full length N symbol crosscorrelation is obtained with multiply-adds using samples in all N symbols of the generated full length N symbol random access channel (RACH) preamble sequence, further wherein the cross-correlation result has a length greater than one symbol; determining a maximum peak magnitude in the full length symbol cross-correlation; identifying a delay corresponding to the determined maximum peak magnitude; and providing a timing advance associated with the delay to the UE to allow synchronization of the communication system.

[0067] Example 16 includes the method of Example 15, further including generating the full length N symbol RACH preamble sequence with a radio unit (RU) of a base station.

[0068] Example 17 includes the method of any of the Examples 15-16, further wherein transmitting full length N symbol RACH preamble sequence to the remote location on a RACH, further includes broadcasting the full length N symbol RACH preamble sequence to the UE with a distributed antenna system (DAS) that is in communication with the base station.

[0069] Example 18 includes the method of any of the Examples 15-17, further including implementing a RACH procedure at the UE that includes transmitting back the full length N symbol RACH preamble sequence.

[0070] Example 19 includes the method of any of the Examples 15-19, wherein each symbol includes a same number of samples.Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that any arrangement, which is calculated to achieve the same purpose, may be substituted for the specific embodiment shown. This application is intended to cover any adaptations or variations of the present invention. Therefore, it is manifestly intended that this invention be limited only by the claims and the equivalents thereof.

Claims

CLAIMS1. A communication system having extended communication coverage using a short random access channel format, the communication system comprising: a base station configured to interface communications between a core network of a service provider and a distributed antenna system (DAS), where the DAS provides a cellular coverage area for user equipment (UE) with a plurality remote antenna units (RAUs); and the base station configured to, generate a full length N symbol random access channel (RACH) preamble sequence of repeated RACH base preambles, each RACH base preamble having a length one symbol; apply a full length N symbol cross-correlation on a received signal from a UE seeking to communicate with the core network through the DAS on the RACH by transmitting a full length N symbol RACH preamble sequence, wherein an output sample in the applied full length N symbol cross-correlation is obtained with multiply-adds using samples in all N symbols of the generated full length N symbol random access channel (RACH) preamble sequence, further wherein the crosscorrelation result has a length greater than one symbol; determine a maximum peak magnitude in the cross-correlation; identify a delay corresponding to the determined maximum peak magnitude; and provide a timing advance associated with the delay to the UE seeking to communicate with the core network to allow the UE seeking to communication with the core network to synchronize communications.

2. The communication system of claim 1, wherein the base station further comprises: at least one radio unit (RU) configured to implement physical layer functions, the at least one RU further configured to identify the delay.

3. The communication system of claim 1, wherein the base station further comprises:a distributed unit (DU) that is in communication with a master unit (MU) of the DAS, the DU configured to implement time critical layer two functions and at least some of the layer one functions for the base station, the DU further configured to identify the delay.

4. The communication system of claim 1, wherein each symbol includes a plurality of samples.

5. The Communication system of claim 1, wherein the cross-correlation produces a base channel impulse response (IR), the delay being identified by a largest magnitude in the base channel IR.

6. The communication system of claim 1, wherein the base station is configured to use ethernet switching in communications between the core network of the service provider and the UE through an extended distribution network provided by the DAS.

7. The communication system of claim 1, wherein the base station further comprises: at least one radio unit (RU) that is in communication with a master unit (MU) of the DAS, the at least one RU configured to implement physical layer functions, the at least one RU further configured to, generate the full length N symbol random access channel (RACH) preamble sequence of repeated RACH base preambles; apply the full length N symbol cross-correlation on a received signal from aUE seeking to communicate with the core network through the DAS on the RACH by transmitting a full length N symbol RACH preamble sequence; determine the maximum peak magnitude in the cross-correlation, identify the delay corresponding to the determined maximum peak magnitude, and provide the timing advance associated with the delay to the UE seeking to communicate with the core network to allow the UE seeking to communication with the core network to synchronize communications;a distributed unit (DU) in communication with the at least one RU, the DU configured to implement time critical layer two functions and at least some of the layer one functions for the base station; and at least one central unit (CU) in communication with the DU, the at least one CU configured to implement layer three and non-time critical functions for the base station, the at least one CU further configured to communicate with the core network of the service provider using an appropriate backhaul network.

8. The communication system of claim 7, wherein the at least one RU includes a plurality of RU antenna ports that are communicatively coupled to MU antenna ports of the MU.

9. A communication system having an extended communication coverage system for short random access channel format, the communication system comprising: a distributed antenna system (DAS) including, a plurality of remote antenna units (RAUs) configured to communicate wirelessly with user equipment via radio frequency (RF) signals; a master unit (MU) in communication with the plurality of RAUs, the MU configured to generate one or more downlink transport signals that are communicated to at least one RAU of the plurality of RAUs and received uplink transport signals from at least one RAU of the plurality of RAUs; a base station including, at least one radio unit (RU) in communication with the MU, the at least oneRU configured to implement physical layer functions and provide an RF interface, the at least one RU further configured to, generate a full length N symbol random access channel (RACH) preamble sequence of repeated RACH base preambles, each RACH base preamble having a length one symbol; apply a full length N symbol cross-correlation on a received signal from a UE seeking to communicate with the core network through the DAS on the RACH by transmitting a full length N symbol RACH preamble sequence, wherein an output sample in the applied full length N symbol cross-correlationis obtained with multiply-adds using samples in all N symbols of the generated full length N symbol random access channel (RACH) preamble sequence, further wherein the cross-correlation result has a length greater than one symbol; determine a maximum peak magnitude in the cross-correlation; identify a delay corresponding to the determined maximum peak magnitude; and provide a timing advance associated with the delay to the UE seeking to communicate with the DAS.

10. The communication system of claim 9, wherein each symbol includes a same number of samples.

11. The Communication system of claim 9, wherein the cross-correlation produces a base channel impulse response (IR), the delay identified by a largest magnitude in the base channel IR.

12. The communication system of claim 9, wherein the at least one RU includes a plurality of RU antenna ports that are communicatively coupled to MU antenna ports of the MU.

13. The communication system of claim 9, wherein the base station is configured to use ethernet switching in communications between the core network of the service provider and the UE through an extended distribution network provided by the DAS.

14. The communication system of claim 9 wherein the base station further comprises: a distributed unit (DU) in communication with the at least one RU, the DU configured to implement time critical layer two functions and at least some of the layer one functions for the base station; and at least one central unit (CU) in communication with the DU, the at least one CU configured to implement layer three and non-time critical functions for the base station, the atleast one CU further configured to communicate with a core network of a service provider using an appropriate backhaul network.

15. A method of operating a communication system having an extended communication coverage system for short random access channel (RACH) format, the method comprising: transmitting a full length N symbol RACH preamble sequence to a remote location, the preamble sequence including a plurality of base preambles, each base preamble having length one symbol; receiving an uplink signal (UL) from a user equipment (UE) at a remote location seeking to communicate over the RACH that includes a full length N symbol RACH preamble sequence; applying a full length N symbol cross-correlation on the received UL signal from the UE, wherein an output sample in the applied full length N symbol cross-correlation is obtained with multiply-adds using samples in all N symbols of the generated full length N symbol random access channel (RACH) preamble sequence, further wherein the crosscorrelation result has a length greater than one symbol; determining a maximum peak magnitude in the full length symbol cross-correlation; identifying a delay corresponding to the determined maximum peak magnitude; and providing a timing advance associated with the delay to the UE to allow synchronization of the communication system.

16. The method of claim 15, further comprising: generating the full length N symbol RACH preamble sequence with a radio unit (RU) of a base station.

17. The method of claim 16, wherein transmitting the full length N symbol RACH preamble sequence to the remote location on a RACH, further comprises: broadcasting the full length N symbol RACH preamble sequence to the UE with a distributed antenna system (DAS) that is in communication with the base station.

18. The method of claim 15, further comprising:implementing a RACH procedure at the UE that includes transmitting back the full length N symbol RACH preamble sequence.

19. The method of claim 15, wherein each base preamble includes one symbol and each symbol includes a plurality of samples.

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