HK1238424B - Remote radio unit and baseband unit for asymetric radio area network channel processing - Google Patents

Description

Remote radio units and baseband units for asymmetric radio area network channel processing

This application claims priority benefit from U.S. patent application serial number 14/578,045, filed December 19, 2014, which is incorporated herein by reference in its entirety.

Technical Field

Embodiments relate to systems, methods, and component arrangements associated with a radio area network (RAN), and one exemplary embodiment specifically relates to an asymmetric centralized, collaborative, or cloud radio access RAN (C-RAN) in which uplink and downlink communication functions and components are asymmetrically configured across remote radio units (RRUs) and baseband units (BBUs) of the C-RAN.

Background Art

Wireless mobile communication technologies use various standards and protocols to transmit data between a base transceiver station (BTS) or Evolved Universal Mobile Telecommunications System (EUMTS) terrestrial radio access node B (eNB) and a wireless mobile device or user equipment (UE). In a centralized, collaborative, or cloud radio access network (C-RAN), the BTS or eNB functionality can be split between the baseband unit (BBU) processing pool and the remote radio equipment (RRE), remote radio unit (RRU), or remote radio head (RRH).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1A illustrates a block diagram showing aspects of a BBU and RRU of a RAN for downlink transmissions, according to an exemplary embodiment.

FIG1B illustrates a block diagram showing aspects of a BBU and RRU of a RAN for uplink transmissions, according to an exemplary embodiment.

FIG2 shows a block diagram of a RAN that can implement asymmetric UL and DL according to an exemplary embodiment.

FIG3 illustrates a method for asymmetric UL and DL in a RAN according to an exemplary embodiment.

FIG4 illustrates an example UE that may be used with an asymmetric RAN according to some embodiments.

5 is a block diagram illustrating an exemplary computer system machine upon which any one or more of the methodologies discussed herein may be executed, according to some embodiments.

DETAILED DESCRIPTION

Embodiments relate to systems, methods, and component devices for radio area networks (RANs), and more particularly to asymmetric RAN architecture and operation. The following description and accompanying figures illustrate specific embodiments to enable those skilled in the art to practice them. Other embodiments may incorporate structural, logical, electrical, methodological, and other variations. Portions and features of some embodiments may be included in or substituted for those of other embodiments. Embodiments recited in the claims include all available equivalents of those claims.

In a C-RAN, the functions of the eNB, which acts as a wireless intermediary between the UE and the network, can be divided between the BBU and the RRU. For example, the BBU can provide digital baseband radio functions, while the RRU can provide analog RF functions. A standard symmetrical architecture for C-RAN is defined by the Common Public Radio Interface (CPRI): Interface Specification V4.2. This symmetrical architecture operates with the BBU and RRU each performing similar corresponding operations for both uplink and downlink communications.

The BBUs and RRUs in a C-RAN can communicate with each other via a physical transport network, such as an optical transport network. This offers the following benefits: Compared to other systems, a C-RAN system can have reduced costs and energy consumption, higher spectral efficiency, and support for multiple standards. This C-RAN can be upgraded using a modular system, where the BBU and RRU components can be upgraded independently, providing system flexibility.

The physical transport network between the RRU and BBU carries a large amount of real-time data and can be a bottleneck on C-RANs with a large number of services. For example, the optical fiber implementation of the physical transport network between the RRU and BBU can carry a large amount of baseband sampling data in real time.

In embodiments with such a physical transport network bottleneck, the architecture can be adjusted to reduce the data rate by reducing digital processing at the BBU, which can reduce the baseband sample data transmitted over the physical transport network. However, in some embodiments, this rearchitecting provides more benefits for uplink communications through the eNB than for downlink communications through the eNB.

As referred to herein, uplink communications refer to communications received at an eNB from a UE, and downlink communications refer to communications sent from an eNB to a UE. Thus, uplink communications in a C-RAN flow from an RRU to a BBU, and downlink communications flow from a BBU to an RRU. The embodiments described herein relate to an asymmetric C-RAN, in which the division of eNB functionality between the BBU and the RRU is different for uplink communications handled by the eNB than for downlink communications handled by the same eNB.

For example, in one embodiment of the eNB for asymmetric C-RAN, all physical layer processing functions may occur at the RRU for downlinks handled by the eNB, with cyclic prefix (CP) and inverse fast Fourier transform processing performed for downlinks handled by the BBU. This reduces the maximum fronthaul downlink rate for the data rate supported by the eNB. In a system with two transmit antennas, two receive antennas, and a 10 MHz system bandwidth, the fronthaul downlink rate would be approximately 100 Mbits per second.

For the uplink in this eNB of an asymmetric C-RAN, CP and Fast Fourier Transform processing can be handled by the RRU instead of the BBU. This creates a different fronthaul rate for the uplink, where the fronthaul uplink rate is determined by frequency-domain I/Q samples. In an implementation with 16-bit I/Q samples, the fronthaul uplink rate would be approximately 700 Mbps, resulting in an asymmetry between the uplink and downlink fronthaul rates.

This asymmetry of having much higher upload rates compared to downlink rates can be particularly useful for frequency division duplex systems. In particular, one disadvantage of the lower rates described above is that in some embodiments, the lower rate links cannot support joint transmission. Frequency division duplex C-RAN systems using beamforming can achieve joint transmission, but the use of joint transmission can be inefficient for downlink communications due to feedback errors that require processor-intensive compensation for downlink communications. Such feedback errors are not a problem in comparable time domain duplex systems. Therefore, for the downlink of a frequency division duplex system, the above-mentioned disadvantage of difficulty in supporting joint transmission is largely eliminated because in many embodiments, joint transmission will not be used due to the inefficiency associated with feedback errors. At the same time, the performance and processing aggregation advantages described for the combined BBU elements of the system are still provided for a frequency division duplex system with rate asymmetry.

Additionally, because downlink signal processing can be simpler than uplink signal processing in certain embodiments, combined uplink receive processing at the BBU of the C RAN allows for more efficient utilization of the BBU's shared resources than systems that perform such processing at individual RRUs. Furthermore, such efficiencies with respect to both BBU receive processing and uplink/downlink processing can provide improved component multipoint (CoMP) performance on links where joint transmit/CoMP performance is enabled.

Figures 1A and 1B show block diagrams of a BBU 110 and an RRU 130, which may be components of an asymmetric C-RAN, according to an exemplary embodiment. Details of how such components fit into a C-RAN are described below with reference to Figure 2. Figure 1A shows downlink circuitry for the BBU 110 and RRU 130, and Figure 1B shows uplink circuitry for the same BBU 110 and RRU 130. The asymmetry between the uplink system of Figure 1B and the downlink system of Figure 1A can be seen in the location of the Fourier transform elements, where an inverse fast Fourier transform (IFFT) 124 in the BBU 110 is used for downlink processing, and a corresponding fast Fourier transform (FFT) 174 in the RRU 130 is used for uplink processing. The asymmetry can also be seen in the CP processing elements and CP processing circuitry, where the add CP 126 processing circuitry is located within the BBU 110, and the corresponding remove CP 176 processing circuitry is located within the RRU 130.

The RRU 130 can be configured to communicate with the BBU 110 over a physical communication link (such as a fiber optic cable in an optical transport network) using a common interface (or shared interface) between the RRU 130 and the BBU 110, such as a CPRI standard interface. Although the CPRI standard defines a symmetric architecture, the standard interface can be configured for an asymmetric system to provide an interface from the BBU 110's added CP 126 in the downlink system to the RRU 130's channel filtering 132, and a different interface with the RRU 130's FFT 174 for transmitting power control and feedback information detection 172 of the BBU 110 in the uplink system.

The RRU 130 can be configured to communicate with the UE over the air interface using a wireless standard such as 3GPP LTE. Other embodiments can use other wireless standards such as WiMAX. The BBU 110 is configured to communicate via the network via backhaul transmission 162. The wireless communication system can be further divided into various sections referred to as layers. In an LTE system, the communication layers may include: a physical (PHY) layer, a media access control (MAC) layer, a radio link control (RLC) layer, a packet data convergence protocol (PDCP) layer, and a radio resource control (RRC) layer. The physical layer may include the basic hardware transmission components of the wireless communication system, such as those used for downlink channel processing as shown in FIG1A and for uplink channel processing as shown in FIG1B.

In downlink channel processing, the eNB may include media access control (MAC) layer and physical (PHY) layer processing elements, such as a MAC layer processor, a channel encoder, a channel interleaver, a channel modulator, a multiple-input multiple-output (MIMO) processor, a transmit power controller, a frame and slot signal generator, an inverse fast Fourier transform (IFFT) modulator, a CP adder, a channel filter, a digital-to-analog converter (DAC), an upconverter, a gain controller, a carrier multiplexer, a power amplifier and a limiter radio frequency (RF) filter, and one or more transmit antennas. As used herein, any description of an eNB (such as the above description) is equally applicable to base transceiver station implementations.

As shown in Figures 1A and 1B, the functions of the eNB can be divided between the BBU 110 and the RRU 130. The BBU 110 can provide radio functions in the digital baseband domain, and the RRU can provide analog radio functions. Compared to the above-mentioned CPRI standard, the BBU 110 can provide similar functions to the radio element controller (REC), and the RRU can provide similar functions to the radio element (RE) or remote radio element (RRE). The BBU 110 can provide radio base station control and management 108. The BBU can also include: backhaul transmission 112 processing; MAC layer 114 processing; channel coding, interleaving and modulation 116; MIMO processing 118; transmit power control 120 for each physical channel; frame and time slot signal generation 122; IFFT 124 modulation; and adding CP 126. The RRU may include channel filtering 132, digital-to-analog (D/A) conversion 134, up-conversion 136, on/off control 138 for each carrier, carrier multiplexing 140, power amplification and limiting 142, and RF filtering 144. In various alternative embodiments, these elements of the BBU 110 may be configured together in any possible manner or separately as part of different system hardware components.

In the uplink channel processing shown in FIG1B , the eNB may include similar or identical elements corresponding to the downlink channel processing unit of FIG1A . Thus, the downlink processing unit of the eNB may include MAC layer and PHY layer processing units, such as one or more receive antennas, RF filters, low noise amplifiers, carrier demultiplexers, automatic gain controllers, down converters, analog-to-digital converters (ADCs), CP removers, fast Fourier transform (FFT) demodulators, transmit power control and feedback information detectors, signal allocation and signal processors, MIMO detectors, channel demodulators, channel deinterleavers, channel decoders, and MAC layer processors. As just described and described above for the downlink, the uplink functionality of the eNB may be divided between the BBU 110 and the RRU 130 .

In the embodiment of Figure 1B, the RRU 130 includes: RF filtering 194, low noise amplification 192, carrier demultiplexing 190, automatic gain control (AGC) 188, down conversion 186, digital-to-analog (D/A) conversion 184, channel filtering 182, CP removal 176 circuitry, and FFT 174 demodulation. The BBU 110 includes: transmit power control and feedback information detection 172; signal distribution to signal processing units 170; MIMO detection 168; channel decoding, deinterleaving, and demodulation 166; MAC layer 164 processing; and backhaul transmission 162 processing circuitry.

In this embodiment of the RRU 130, the channel filtering 132 module operates in conjunction with the digital-to-analog conversion module, frequency conversion module, gain control module, carrier multiplexing module, amplification module, and filtering module for downlink channel processing. The digital-to-analog conversion module may include a digital-to-analog converter (DAC) 134 for downlink channel processing or an analog-to-digital converter (ADC) 184 for uplink channel processing. The conversion module may include an upconverter 136 for downlink channel processing or a downconverter 186 for uplink channel processing. When the CP remover is located within the RRU, a random access channel (RACH) 182 processing module or circuitry may be used for uplink channel processing. The physical random access channel (PRACH) or random access channel (RACH) may be used for initial UE access to the RAN and when the UE loses its uplink synchronization. The gain control module may include an on/off controller for each carrier 138 for downlink channel processing or an automatic gain controller (AGC) 188 for uplink channel processing. The carrier multiplexing module 140 may include a carrier multiplexer for downlink channel processing or a carrier demultiplexer 190 for uplink channel processing. The amplification module may include a power amplifier and limiter 142 for downlink channel processing or a low noise amplifier 192 for uplink channel processing. The filtering module may include a radio frequency filter 144 or 194.

As described above, one way to reduce the amount of data transmitted between the RRU and BBU is to perform Fourier transform processing at different locations. For orthogonal frequency division multiplexing signals using the uplink and downlink processing described in Figures 1A and 1B, the Fourier transform processing transforms the signals in a manner that affects the amount of data associated with the signals. For downlink communications, the IFFT 124 transforms the downlink communications from frequency-domain signals to time-domain signals for communication using the air interface. For uplink communications, the FFT 174 transforms the uplink communications received from the air interface from time-domain signals to frequency-domain signals. Thus, the physical link between the RRU 130 and the BBU 110 shown in Figure 1A transmits downlink communications as time-domain signals, and the physical link shown in Figure 1B transmits uplink communications as frequency-domain signals. The asymmetry between the communications represented by the time-domain signals compared to the communications represented by the frequency-domain signals may result in different loads on the physical communication link between the BBU 110 and the RRU 130.

Another way to reduce the amount of data transmitted between the RRU and BBU is to move the CP module from the BBU to the RRU. CP is an additional amount of data added to the signal. By removing the CP from downlink communications at the RRU, the amount of data sent over the physical communication link is reduced. In some embodiments, the data and overhead associated with the CP can be approximately 7% of the data associated with downlink communications, and removing the CP from downlink communications at the RRU can reduce downlink communication bandwidth consumption by a corresponding 7%. In other embodiments, different benefits may be seen depending on the system characteristics associated with the CP.

As discussed in the initial example, cyclic prefix (CP) and inverse fast Fourier transform (IFFT) processing are used for the downlink, which is handled by the BBU. This reduces the maximum fronthaul downlink rate for the data rates supported by the eNB. In a system with two transmit antennas, two receive antennas, and a 9-11 MHz system bandwidth, the fronthaul downlink rate would be approximately 90-110 Mbps. For the uplink in such an eNB with asymmetric C-RAN, CP and IFFT processing can be handled by the RRU instead of the BBU. This creates a different fronthaul rate for the uplink, where the fronthaul uplink rate is determined by frequency-domain I/Q samples. In an embodiment with 16-bit I/Q samples, the fronthaul uplink rate would be approximately 600-800 Mbps, resulting in an asymmetry between the uplink and downlink fronthaul rates. Other fronthaul rates may result in other embodiments or system designs with different numbers of antennas and different system bandwidths. The asymmetry in the fronthaul rates arises from the architectural differences shown in FIG1A and FIG1B , where the CP 176 and FFT 174 circuitry within the RRU 130 is removed as part of the uplink functionality shown in FIG1B in order to reduce the amount of data transmitted between the RRU 130 and the BBU 110. However, the corresponding circuitry for the downlink functionality of FIG1A , which adds the CP 126 and IFFT 124 circuitry, remains within the BBU 110 in order to utilize the shared resources of a centralized set of baseband units, which may include the BBU 110, in the baseband processing pool 210 shown in FIG2 .

FIG2 then illustrates aspects of an exemplary C-RAN 200 that can be used to implement asymmetric functionality between BBU and RRU elements, as described with respect to BBU 110 and RRU 130. C-RAN 200 can provide centralized processing, collaborative radio, and a real-time cloud infrastructure RAN. Centralized signal processing can significantly reduce the number of on-site equipment rooms required to cover the same area as a traditional RAN. Collaborative radio using distributed antennas equipped by remote radio units (RRUs) can provide higher spectral efficiency than a traditional RAN. A real-time cloud infrastructure based on an open platform and eNB virtualization enables aggregation and dynamic allocation of processing power, which can reduce power consumption and increase infrastructure utilization. C-RAN 200 can provide end users with reduced costs and lower energy consumption, higher spectral efficiency, support for multiple standards and smooth evolution, and better Internet services.

In particular, one characteristic of mobile networks is that mobile devices often move from one place to another. The movement of mobile devices can have a time-geometric trend. For example, during working hours, a large number of mobile devices move from residential areas to central office areas and industrial areas for work. In the evening or non-working hours, mobile devices move back to residential areas (e.g., homes) or entertainment areas. Therefore, the network load moves in a similar pattern in the mobile network. The processing capacity of each eNB can be used by active mobile devices within the cell range of the eNB. When a mobile device moves outside the cell range of the eNB, the eNB can remain idle, with most of the processing capacity of the eNB wasted. Compared to what is possible in a RAN where the BBU and RRU elements are tightly coupled, the C-RAN architecture can allow the remote pool of RRUs to more extensively utilize the portion of the eNB processing located at the BBU.

C-RAN 200 in FIG2 includes a remote wireless battery 230, a baseband processing pool 210, and a physical communication network 220 connecting the baseband processing pool 210 and the remote wireless battery 230. The remote wireless battery 230 includes a plurality of remote radio units (RRUs) 233A-1 having antennas. The baseband processing pool 210 includes baseband units (BBUs) 212A-C. The physical transport network, implemented as the physical communication network 220, includes physical communication links 222A-D. The physical communication network 220 connects at least one RRU in the remote wireless battery 230 to at least one BBU in the baseband pool 210. In embodiments where the physical communication network 220 is an optical communication network, the physical communication links 222A-D may each be an optical communication link.

The baseband processing pool 210 can be centralized. Each BBU in the baseband processing pool 210 can include a high-performance general-purpose processor, a real-time virtualized processor, and/or a physical (PHY) layer processor and/or a MAC layer processor 214A-F. The BBU can be coupled to the load balancer and switches 218A-B via electrical or optical cables 226. In various embodiments, the physical communication network 220 can be a low-latency transmission network, a bandwidth-efficient network, and/or an optical transmission network using optical fibers or optical cables. In another example, the physical communication network 220 can be a high-speed power transmission network. The physical communication network 220 can provide a physical communication link between the BBUs 212A-C and the RRUs 232A-I. The physical communication network 220 can include optical fiber links, wired power links, or both. The physical communication link can use aspects of the CPR1 standard or a custom interface. In the CPR1 standard, the BBU can be referred to as a radio element controller (REC). The RRU can be referred to as a remote radio head (RRH), remote radio equipment (RRE), or radio equipment (RE). Each RRU of the remote wireless cell 230 can be separated by a selected distance from the BBU of the baseband processing pool 210. Each RRU can include a sector, cell, or coverage area 238 for a mobile device, such as user equipment (UE) 234A-J, where a mobile device can be located within multiple sectors, cells, or coverage areas. The distributed RRUs comprising the remote wireless cell 230 of the C-RAN 200 can provide high capacity and wide coverage areas for the RAN.

RRU 232A-1 can be smaller than BBU 212A-C, easier to install, easier to maintain, and consume less power. Baseband processing pool 210 can aggregate the processing power of BBUs using real-time virtualization technology and provide signal processing capabilities to virtual eNBs or RRUs in the pool. Physical communication network 220 can distribute processed signals to RRUs in remote radio cells 230. The centralized baseband processing pool 210 can reduce the number of eNB rooms used for BBUs and enable resource aggregation and large-scale coordinated radio transmission/reception. The eNB room can be the equipment room for the BBU that houses the baseband processing pool 210 and other eNB processing equipment.

The physical communication link can use CPRI. The radio element controller (REC) can include the radio functions of the digital baseband domain, and the radio element (RE) can include the analog radio frequency functions. The functions divided between the two parts can be performed so that a common interface based on in-phase and quadrature-phase (IQ or I/Q) data can be defined. The CPRI standard interface communication structure can be used to transmit IQ samples between the REC (or BBU) and the RE (or RRU). For WiMAX, the REC can provide access to network entities (e.g., other BSs or access service network gateways (ASN-GW)), and the RE can be used as an air interface to the subscriber station (SS) and/or mobile subscriber station (MSS). For the Evolved Universal Terrestrial Radio Access (E-UTRA) network, UTRAN or Evolved UTRAN (eUTRAN) used in 3GPP LTE, the REC can provide access to the Evolved Packet Core (EPC) through the SI interface for transmitting user plane and control plane services, and the RE can be used as an air interface to the UE.

For asymmetric C-RAN, the physical communication network 220 (such as an optical transport network) can use separate interface settings for uplink and downlink communications, which can be customized or standards-based. In some embodiments, a radio base station control and management system within the baseband pool 210 can be used to manage the separate interface settings for uplink and downlink communications. In some embodiments, this can be the radio base station control and management 108 of the BBU 110 that is part of the baseband pool 210.

The physical communication network 220 can act as a bottleneck on a C-RAN with a large amount of mobile Internet traffic. The optical fiber of the physical transmission network between the RRU and the BBU can transmit a large amount of baseband sample data in real time. For example, in a 20 MHz frequency division duplex (FDD) four-antenna deployment, with 16 bits per I/Q sample and 8B/10B line coding, the rate on the optical fiber (or optical fiber link rate) is 4x 16x 2x 10/8x 30.72M = 4.915 Gigabits per sample (Gbps) (4 antennas x 16 bits per I/Q sample x 2 bits per I/Q data x 10/8 bits of line coding x 30.72 megabits (Mb) per sample of the LTE sampling rate). The optical fiber link rate (also referred to as the CPRI rate when using the CPRI standard interface) can be the data rate on the optical fiber or cable of the physical transmission network. Supporting more advanced features such as carrier aggregation or more antennas (e.g., eight antennas) can significantly increase the data rate on the physical transmission network. The high data rate between REC and RE for real-time transmission of baseband sampling data can reduce the cost-effectiveness of the C-RAN architecture.

Three different approaches can be used to handle the high data rates of the physical transport network. In the first approach, data compression techniques such as reducing the number of bits/sample or nonlinear quantization can be used, which can reduce performance (using simple quantization) or increase complexity. Second, the fiber network can be upgraded to provide wavelength division multiplexing (WDM), which can increase the cost of the physical transport network and C-RAN. Third, the data transmitted through the physical transport network can be reduced by reducing the digital processing at the BBU and/or the amount of baseband sampled data transmitted through the physical transport network. Moving the CP circuit and/or the FFT circuit can reduce the fiber link rate, where the minimum performance complexity is located at the RRU.

3 then describes an exemplary embodiment of a method for performing channel processing on an RRU in a RAN, shown as method 300. For illustrative purposes, method 300 is described with respect to the elements of BBU 110, RRU 130, and RAN 200 discussed above. In other embodiments, other implementations of the RAN, RRU, and BBU may be used to perform different methods of asymmetric communication using the RAN.

Operation 302 involves receiving an uplink frame at the RRU 130 from a first user equipment (UE). A frame may be considered a unit of communication for any uplink or downlink communication described herein. As described above and in more detail below, such uplink communication may utilize any wireless communication standard or wireless communication method. The UE involved in operation 302 may be similar to UE 234A-I, UE 400 described below with respect to FIG. 4 , or any other such UE.

Operation 304 involves processing the uplink frame at the RRU 130 to remove the uplink CP. In various embodiments, a CP, or cyclic prefix, represents a guard period at the beginning of a symbol that provides protection against multiple mathematical delay spreads. Such a CP can be generated by copying the end of a symbol that is part of a communication to a starting prefix preceding the symbol. Thus, removing the first CP from the uplink communication includes removing the starting prefix preceding the symbol that matches the end of the symbol that constitutes at least a portion of the uplink communication. The uplink communication includes at least a single symbol with a cyclic prefix, but may include any number of symbols, at least some of which have a CP when received by the RRU 130. Operation 304 may be performed by Remove CP 176, which may be implemented as a CP remover circuit within the CP processing circuitry of the RRU 130.

Operation 306 involves performing a fast Fourier transform on the uplink frame without the uplink CP to generate a frequency domain signal. Any known circuit for performing a fast Fourier transform may be used in conjunction with operation 306 so that the processing speed associated with the FFT is sufficient for the communication speed of the relevant link.

Operation 308 involves transmitting the uplink communication after the fast Fourier transform to the BBU 110 via the physical communication network 220. As described above, the physical communication network 220 can be an optical communication link having an interface defined by the CPRI standard. In various additional embodiments where multiple symbols are processed as part of one or more uplink communications, different uplink communications can be sent to different BBUs that are part of the baseband processing pool 210 that includes the BBU 110, and the load balancer and switch 218 can assist in selecting the different BBUs that include the BBU 110 from among the BBUs in the baseband processing pool 210.

Operation 310 involves receiving a downlink frame from the BBU 110 at the RRU 130 via the physical communication network 220, wherein the downlink frame includes a downlink CP. Similar to the uplink frame described above, the downlink frame consists of one or more symbols, wherein at least a portion of the symbols are preceded by a CP. Operation 312 includes transmitting the downlink communication to the UE without processing the downlink frame at the RRU to perform an FFT or adjust the downlink CP of the downlink frame. Thus, in certain embodiments, the asymmetry of the system's execution of method 300 can be characterized as the CP and FFT/IFFT processing being performed separately by the RRU 130 for uplink communication and the BBU 110 for downlink communication. This may be contrasted with a symmetric approach in which the CP and FFT/IFFT processing are performed by the RRU for both uplink and downlink communication, or by the BBU for both uplink and downlink communication.

Various additional methods may be operated in conjunction with the above-described method 300. These methods may each include the operation of receiving a signal at an RRU from a baseband unit (BBU) over a physical communication link, wherein the BBU is configured for medium access control (MAC) layer processing and the RRU is configured to communicate with a wireless mobile device over an air interface.

Such methods may operate with an RRU including radio frequency (RF) filtering circuitry, wherein different downlink RF filtering 144 and uplink RF filtering 194 circuitry or configurations are used for frequency division duplex communication, in which uplink communication uses a different frequency than downlink communication. Such methods may additionally operate with an RRU 130 including multiple transmit antennas and multiple receive antennas, wherein the RRU 130 is configured such that uplink communication comprises a joint transmit communication. Such methods may additionally operate where downlink communication is not a joint transmit communication, or where the RRU 130 is not configured or capable of sending downlink communication as a joint transmit communication. Similar methods may operate with an RRU 130 also including multiple transmit antennas and multiple receive antennas, wherein the RRU is further configured such that uplink communication is part of an uplink joint transmission. Further, such methods may operate where the RRU 130 is further configured such that downlink communication is not part of a downlink joint transmission.

One implementation of such an RRU may operate with a system bandwidth between 9-11 MHz, a downlink rate between 90 Mbps and 110 Mbps from the BBU, a frequency domain I/Q sampling rate of 16 bits, and an uplink rate between 600 Mbps and 800 Mbps to the BBU. Additional alternative embodiments may operate with different settings.

Additional instances of the RRU 130 may operate with a random access channel (RACH) processing module 182 for uplink channel processing.

In addition to the method 300 performed by the RRU 130, a corresponding method may also be performed by the BBU 110. In this method, the BBU 110 enables communication between a device on the network and a UE via the RRU 130. Before the BBU 110 sends a downlink communication to the RRU 130, the downlink communication has a CP added by the add CP 126 module of the BBU 110. Before the uplink communication is received at the BBU 110, the uplink communication received from the RRU 130 has the CP removed by the RRU 130.

The BBU 110 may operate with the following CP processing circuitry, wherein the CP processing circuitry includes CP addition 126 circuitry that adds CP to downlink communications. Additionally, the BBU 110 may operate in an additional embodiment of this method, wherein, before adding the CP 126 and after receiving the signal from the network at the BBU 110 via the backhaul transmission 112, an inverse fast Fourier transform (IFFT) 124 circuitry processes the orthogonal frequency division multiplexing (OFDM) symbols into a modulated signal using an inverse fast Fourier transform (IFFT) 124 modulator. In an asymmetric system, the BBU 110 may not use a modulator or other FFT circuitry to perform FFT processing on uplink communications and may instead perform such FFT uplink processing at an RRU, such as the RRU 130.

Another operation of the method may include generating a frame and time slot signal using a frame and time slot signal generation 122 module prior to IFFT 124 processing and after receiving the signal. Operations of a multiple-input multiple-output (MIMO) processing 118 circuit may also be included for separating a channel data stream into multiple MIMO data streams for multiple antenna ports using a MIMO processor and controlling the transmit power of each physical channel 120 module using a transmit power controller. Another operation of the method may include encoding binary input data for a channel using one or more modules of a channel encoder, interleaving the encoded data using a channel interleaver, and modulating the interleaved data, which is shown as channel encoding, interleaving, and modulation 116. In some embodiments, this places the downlink communication into a channel data stream using a channel modulator prior to MIMO processing 118.

Although the above methods and block diagrams illustrate various operations performed by device circuits including circuits of the BBU 110 and the RRU 130 , physical layer operations or circuit elements may be located and performed between the above-described main elements.

In various embodiments, a C-RAN, such as a C-RAN 200 having an asymmetric system of BBUs 110 and RRUs 130, may be used to enable wireless communications with various UEs, which may be mobile devices such as laptops, cellular phones, tablets, and other such computers. FIG4 provides an exemplary diagram of a UE 400. The UE may include one or more antennas configured to communicate with a transmitting station, such as a base station (BS), an evolved node B (eNB), a RU, or other types of wireless wide area network (WWAN) access points. The mobile device may be configured to communicate using at least one wireless communication standard including 3GPP LTE WiMAX, high-speed packet access (HSPA), Bluetooth, and WiFi. The mobile device may communicate using a separate antenna for each wireless communication standard, or a shared antenna for multiple wireless communication standards. The mobile device may communicate in a wireless local area network (WLAN), a wireless personal area network (WPAN), and/or a WWAN.

FIG4 illustrates an example of a UE 400. UE 400 may be any mobile device, mobile station (MS), mobile wireless device, mobile communication device, tablet computer, handset, or other type of mobile wireless computing device. UE 400 may include one or more antennas 408 within a housing 402 configured to communicate with a hotspot, base station (BS), eNB, or other type of WLAN or WPAN access point. Thus, the UE may communicate with a WAN, such as the Internet, via an eNB or base station transceiver implemented as part of an asymmetric RAN as described above. UE 400 may be configured to communicate using multiple wireless communication standards, including standards selected from 3GPP LTE, WiMAX, High Speed Packet Access (HSPA), Bluetooth, and Wi-Fi standard definitions. UE 400 may communicate using separate antennas for each wireless communication standard, or shared antennas for multiple wireless communication standards. UE 400 may communicate in a WLAN, WPAN, and/or WPAN.

FIG4 also shows a microphone 420 and one or more speakers 412 that can be used to input or output audio from the UE 400. The display screen 404 can be a liquid crystal display (LCD) screen or other type of display screen, such as an organic light emitting diode (OLED) display. The display screen 404 can be configured as a touch screen. The touch screen can use capacitive, resistive, or other types of touch screen technology. The application processor 414 and the graphics processor 418 can be coupled to the internal memory 416 to provide processing power and display capabilities. The non-volatile memory port 410 can also be used to provide data input/output options to the user. The non-volatile memory port 410 can also be used to expand the memory capacity of the UE 400. The keyboard 406 can be integrated with the UE 400 or wirelessly connected to the UE 400 to provide additional user input. A touch screen can also be used to provide a virtual keyboard. A camera 422 located on the front (display) side or rear side of the UE 400 can also be integrated into the housing 402 of the UE 400. Any such elements may be used in order to generate information that may be transmitted as uplink data over an asymmetric C-RAN and to receive information that may be transmitted as downlink data over an asymmetric C-RAN as described herein.

5 is a block diagram illustrating an exemplary computer system machine 500 on which any one or more methods discussed herein may be run. The computer system machine 500 may be embodied as a UE 400, a BBU 110, an RRU 130, or any other computing platform or element described or referenced herein. Additionally, aspects of the computer machine 500 may be integrated with any BBU, RRU, or elements of a BBU or RRU (such as BBU 110 and RRU 130). In various alternative embodiments, the machine may operate as a standalone device or may be connected (e.g., networked) to other machines. In a networked deployment, the machine may operate as a server or client machine in a server-client network environment, or it may act as a peer machine in a peer-to-peer (or distributed) network environment. The machine may be a personal computer (PC) that may or may not be portable (e.g., a laptop or netbook computer), a tablet computer, a set-top box (STB), a game console, a personal digital assistant (PDA), a mobile phone or smartphone, a network appliance, a network router, a switch or bridge, or any machine capable of executing instructions (sequential or otherwise) that specify the operations to be taken by the machine. Further, while only a single machine is shown, the term "machine" shall also be construed to include any collection of machines that individually or collectively execute one (or more) sets of instructions to perform any one or more of the methodologies discussed herein.

The exemplary computer system machine 500 includes a processor 502 (e.g., a central processing unit (CPU), a graphics processing unit (GPU), or both), a main memory 504, and a static memory 506, which communicate with each other via an interconnect 508 (e.g., a link, a bus, etc.). The computer system machine 500 may also include a video display unit 510, an alphanumeric input device 512 (e.g., a keyboard), and a user interface (UI) navigation device 514 (e.g., a mouse). In one embodiment, the video display unit 510, the input device 512, and the UI navigation device 514 are touch screen displays. The computer system machine 500 may additionally include a storage device 516 (e.g., a drive unit), a signal generating device 518 (e.g., a speaker), an output controller 532, a power management controller 534, and a network interface device 520 (which may include or be in operable communication with one or more antennas 530, transceivers, or other wireless communication hardware), as well as one or more sensors 528, such as a global positioning sensor (GPS) sensor, a compass, a position sensor, an accelerometer, or other sensors.

The storage device 516 includes a machine-readable medium 522 on which is stored one or more sets of data structures and instructions 524 (e.g., software) embodying or utilized by any one or more of the methodologies or functionality described herein. The instructions 524, when executed by the computer system machine 500, may also reside, completely or at least partially, within the main memory 504, the static memory 506, and/or within the processor 502, with the main memory 504, the static memory 506, and the processor 502 also constituting machine-readable media.

Although the machine-readable medium 522 is shown as a single medium in the exemplary embodiment, the term "machine-readable medium" may include a single medium or multiple media (e.g., a centralized or distributed database, and/or associated cache memories and servers) that store one or more instructions 524. The term "machine-readable medium" should also be understood to include any tangible medium that can store, encode, or transmit instructions for execution by a machine and that causes the machine to perform any one or more of the methods of the present disclosure, or that can store, encode, or transmit data structures utilized by such instructions or associated with such an instruction set.

Instructions 524 may also be transmitted or received using transmission media over a communications network 526 via a network interface device 520 utilizing any of a number of well-known transfer protocols (e.g., HTTP). The term "transmission media" shall be understood to include any intangible medium capable of storing, encoding, or transmitting instructions for execution by a machine, including digital or analog communications signals or other intangible media to facilitate communication of such software.

Various technologies, or some aspects or parts thereof, can take the form of program codes (i.e., instructions) embodied in tangible media, such as floppy disks, CD-ROMs, hard drives, non-transitory computer-readable storage media, or any other machine-readable storage media, wherein when the program code is loaded into a machine such as a computer and executed by it, the machine becomes a device for practicing various technologies. When the program code is executed on a programmable computer, the computing device may include a processor, a storage medium (including volatile and non-volatile memory and/or storage elements) readable by the processor, at least one input device, and at least one output device. Volatile and non-volatile memory and/or storage elements may be RAM, EPROM, flash drives, optical drives, magnetic hard drives, or other media for storing electronic data. Base stations and mobile stations may also include transceiver modules, counter modules, processing modules, and/or clock modules or timer modules. One or more programs that can implement or utilize the various technologies described herein may use application programming interfaces (APIs), reusable controls, etc. Such programs may be implemented in high-level programs or object-oriented programming languages to communicate with computer systems. However, if desired, the program could be implemented in assembly or machine language. In any case, the language could be a compiled or interpreted language and combined with hardware implementations.

Although the foregoing examples of wireless network connections are provided above with specific reference to 3GPP LTE/LTE-A, IEEE 802.11, and Bluetooth communication standards, it will be understood that various other WWAN, WLAN, and WPAN protocols and standards can be used in conjunction with the technology described herein. These standards include, but are not limited to, other standards from 3GPP (e.g., HSPA+, UMTS), IEEE 802.16 (e.g., 802.16p), or Bluetooth (e.g., Bluetooth 4.0 or a similar standard defined by the Bluetooth Special Interest Group) standard series. Other applicable network configurations may be included within the scope of the communication network currently described. It will be understood that any number of personal area networks, LANs, and WANs, using any combination of wired or wireless transmission media, can be used to facilitate communications on such communication networks.

The above embodiments may be implemented in one or a combination of hardware, firmware, and software. Various methods or techniques, or aspects or portions thereof, may take the form of program code (i.e., instructions) embodied in a tangible medium, such as flash memory, a hard drive, a portable storage device, a read-only memory (ROM), a random access memory (RAM), a semiconductor memory device (e.g., an electrically programmable read-only memory (EPROM), an electrically erasable programmable read-only memory (EEPROM)), a magnetic disk storage medium, an optical storage medium, and any other machine-readable storage medium or storage device, wherein when the program code is loaded into and executed by a machine (such as a computer or a networked device), the machine becomes an apparatus for practicing the various techniques.

Machine-readable storage media or other storage devices may include any non-transitory mechanism for storing information in a machine (e.g., computer) readable form. When program code is executed on a programmable computer, computing means may include a processor, a storage medium (including volatile and non-volatile memory and/or storage element) that can be read by the processor, at least one input device, and at least one output device. One or more programs that can implement or utilize the various technologies described herein can use application programming interfaces (APIs), reusable controls, etc. Such programs may be implemented in high-level programs or object-oriented programming languages to communicate with computer systems. However, if desired, the program can be implemented in assembly or machine language. In any case, language can be compiled or interpreted language, and can be combined with hardware implementation schemes.

It should be understood that the functional units or capabilities described in this specification may be referred to or labeled as components or modules in order to more specifically emphasize their implementation independence. For example, components or modules may be implemented as hardware circuits (including customized very large scale integration (VLSI) circuits or gate arrays), off-the-shelf semiconductors (such as logic chips, transistors), or other discrete components. Components or modules may also be implemented in programmable hardware devices (such as field programmable gate arrays, programmable array logic, programmable logic devices, etc.). Components or modules may also be implemented in software for execution by various types of processors. For example, an identified component or module of executable code may include one or more physical or logical blocks of computer instructions, such as those that may be organized as objects, processes, or functions. However, the executable portions of the identified components or modules need not be physically located together, but may include different instructions stored in different locations that, when logically combined together, constitute the component or module and achieve the specified purpose of the component or module.

In fact, the parts or modules of executable code can be single instructions or many instructions, and even can be distributed on several different code segments, in different programs and on several memory devices.Similarly, in this article, operational data can be identified and illustrated in parts or modules, and may embody and be organized in the data structure of any suitable type in any suitable form.Operational data can be collected as a single data set, or can be assigned to different locations (being included on different storage devices), and can only be present in a system or network as an electronic signal at least in part.Parts or modules can be passive or active, including the agent that can be operated to perform desired function.

Additional examples of the presently described method, system, and apparatus embodiments include the following non-limiting configurations. Each of the following non-limiting examples may exist independently or may be combined in any permutation or combination with any one or more other examples provided below or throughout this disclosure.

Claims (23)

1. A remote radio unit (RRU) including hardware processing circuitry, configured to: Receive uplink communication from user equipment (UE) via air interface; The uplink communication is converted from an uplink time-domain signal to an uplink frequency-domain signal; The uplink frequency domain signal is transmitted to the baseband unit (BBU) via a physical communication link; and Downlink communication is received from the BBU via the physical communication link, and the downlink communication includes downlink time-domain signals; Uplink communication is transmitted and downlink communication is received via an asymmetric uplink and downlink configuration. 2. The RRU according to claim 1, further comprising: Circuitry configured to remove the uplink cyclic prefix (CP) from the uplink communication; and Uplink radio frequency (RF) filtering circuit and downlink RF filtering circuit, wherein the RRU is further configured to communicate with the UE via the air interface including frequency division duplex communication; The conversion from the uplink time-domain signal to the uplink frequency-domain signal is performed by applying a Fast Fourier Transform to the uplink communication; and The downlink communication received from the BBU includes downlink CP. 3. The RRU of claim 2, wherein the RRU is further configured such that the downlink communication is not part of a downlink joint transmission. 4. The RRU of claim 2, wherein the RRU is further configured with a system bandwidth between 9 and 11 MHz, a downlink rate between 90 Mbps and 110 Mbps from the BBU, a 16-bit frequency domain I/Q sampling rate, and an uplink rate between 600 Mbps and 800 Mbps to the BBU. 5. The RRU according to claim 1, further comprising random access channel (RACH) processing circuitry for uplink channel processing. 6. The RRU of claim 1, further comprising modulation circuitry, wherein the modulation circuitry includes an FFT circuitry to perform the FFT on the uplink communication, and wherein the modulation circuitry is not configured to perform an inverse fast Fourier transform on the downlink communication. 7. The RRU of claim 1, further comprising optical input and output, wherein the physical communication link comprises an optical transmission network. 8. The RRU of claim 1, wherein the RRU is configured as the first RRU of a plurality of RRUs in a cloud radio access network. 9. The RRU of claim 1, wherein the RRU is configured to communicate with the BBU, which is part of the baseband processing pool, via a load balancer and a switch. 10. The RRU of claim 2, wherein the downlink CP of the downlink communication is added to the downlink communication by the BBU, wherein the downlink communication is processed by the inverse FFT circuit of the BBU and output as the downlink time-domain signal, and wherein the RRU is not configured to add the downlink CP to the downlink communication. 11. The RRU of claim 1, further comprising an RRU with multiple transmit antennas and multiple receive antennas, wherein the RRU is further configured such that the uplink communication is part of an uplink joint transmission. 12. A baseband unit (BBU) including hardware processing circuitry, configured to: Receive downlink communication from the backhaul transmission network; Perform an inverse fast Fourier transform on the downlink communication to convert the downlink communication into a downlink time-domain signal; After converting the downlink communication into the downlink time-domain signal, a downlink cyclic prefix (CP) is added to the downlink communication; The downlink time-domain signal is transmitted to the remote radio unit (RRU) via a physical communication link; and Uplink communication is received from the RRU via the physical communication link, wherein the uplink communication includes frequency domain signals and wherein the uplink communication does not include uplink CP; Downlink communication is transmitted and uplink communication is received via an asymmetric uplink and downlink configuration. 13. The BBU of claim 12, further comprising modulation circuitry, wherein the modulation circuitry includes an inverse fast Fourier transform modulator circuitry performing the inverse fast Fourier transform, wherein the modulation circuitry is not configured for fast Fourier transform processing, wherein the uplink communication received from the RRU is processed by the fast Fourier transform circuitry of the RRU, and wherein the uplink CP is removed from the uplink communication by the CP removal circuitry of the RRU. 14. The BBU of claim 13, further comprising: Frame and time-slot signal generation circuitry for downlink channel processing; and Signal distribution and signal processing circuitry used for uplink channel processing. 15. The BBU of claim 14, further comprising: The transmit power control circuit is configured to perform power control for each physical channel for downlink channel processing and to perform feedback information detection for uplink channel processing. 16. The BBU of claim 15, further comprising a multiple-input multiple-output (MIMO) system configured for MIMO processing as part of downlink channel processing and MIMO detection as part of uplink channel processing. 17. The BBU of claim 16, further comprising: A channel coding circuit, wherein the channel coding circuit includes a channel encoder for downlink channel processing and a channel decoder for uplink channel processing; A channel interleaving circuit, wherein the channel interleaving circuit includes a channel interleaver for downlink channel processing and a channel deinterleaving circuit for uplink channel processing; and A channel modulation circuit, wherein the channel modulation circuit includes a channel modulator for downlink channel processing and a channel demodulator for uplink channel processing. 18. A method for channel processing of remote radio units (RRUs) in a radio access network (RAN), comprising: Uplink frames are received from the first user equipment (UE) at the RRU; The RRU processes the uplink frame to remove the uplink CP; Perform a Fast Fourier Transform on the uplink frame that does not have the uplink CP to generate a frequency domain signal; After the Fast Fourier Transform, the uplink communication is transmitted to the baseband unit (BBU) via a physical communication link; The RRU receives downlink communication from the BBU via the physical communication link, wherein the downlink communication includes a downlink CP; and The downlink communication is transmitted to the UE without being processed by the RRU, so as to adjust the downlink CP of the downlink communication; Uplink communication is transmitted and downlink communication is received via an asymmetric uplink and downlink configuration. 19. The method of claim 18, wherein the interface for the uplink communication is defined by the Common Radio Interface (CPRI): Interface Specification. 20. A method for channel processing of remote radio units (RRUs) in a radio access network (RAN), comprising: Receive uplink frames from user equipment (UE) via air interface; The uplink frame is converted from an uplink time-domain signal to an uplink frequency-domain signal; The uplink frequency domain signal is transmitted to the baseband unit (BBU) via a physical communication link; and The downlink frame, which includes a downlink time domain signal, is received from the BBU via the physical communication link. Uplink frames are transmitted and downlink frames are received via an asymmetric uplink and downlink configuration. 21. The method of claim 20, further comprising: The uplink frame is received from the first user equipment (UE) at the RRU; The RRU processes the uplink frame so that the uplink CP is removed using the RRU's CP remover circuitry; A fast Fourier transform is performed on the uplink frame without the uplink CP using a modulator in order to generate the uplink frequency domain signal; After the Fast Fourier Transform, the uplink frame is transmitted to the BBU via the physical communication link. The downlink frame is received from the BBU via the physical communication link at the RRU, wherein the downlink frame includes a downlink CP added to the downlink frame by the CP addition circuit of the BBU, and wherein the downlink frame includes a time-domain signal processed by the inverse fast Fourier transform circuit of the BBU. 22. The method of claim 21, further comprising: transmitting the downlink frame to the UE without processing the downlink frame in the RRU, so as to adjust the downlink CP of the downlink frame and without processing the downlink frame through the modulator. 23. A non-transitory computer-readable medium comprising instructions that, when executed by one or more processors, cause a device to perform the method of any one of claims 18-22.