Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
  • H04B10/25—Arrangements specific to fibre transmission
  • H04B10/2575—Radio-over-fibre, e.g. radio frequency signal modulated onto an optical carrier
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04J—MULTIPLEX COMMUNICATION
  • H04J3/00—Time-division multiplex systems
  • H04J3/16—Time-division multiplex systems in which the time allocation to individual channels within a transmission cycle is variable, e.g. to accommodate varying complexity of signals, to vary number of channels transmitted
  • H04J3/1605—Fixed allocated frame structures
  • H04J3/1611—Synchronous digital hierarchy [SDH] or SONET
  • H04J3/1617—Synchronous digital hierarchy [SDH] or SONET carrying packets or ATM cells
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
  • H04B10/27—Arrangements for networking
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04J—MULTIPLEX COMMUNICATION
  • H04J3/00—Time-division multiplex systems
  • H04J3/16—Time-division multiplex systems in which the time allocation to individual channels within a transmission cycle is variable, e.g. to accommodate varying complexity of signals, to vary number of channels transmitted
  • H04J3/1605—Fixed allocated frame structures
  • H04J3/1652—Optical Transport Network [OTN]
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04J—MULTIPLEX COMMUNICATION
  • H04J2203/00—Aspects of optical multiplex systems other than those covered by H04J14/05 and H04J14/07
  • H04J2203/0001—Provisions for broadband connections in integrated services digital network using frames of the Optical Transport Network [OTN] or using synchronous transfer mode [STM], e.g. SONET, SDH
  • H04J2203/0057—Operations, administration and maintenance [OAM]
  • H04J2203/006—Fault tolerance and recovery
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04J—MULTIPLEX COMMUNICATION
  • H04J2203/00—Aspects of optical multiplex systems other than those covered by H04J14/05 and H04J14/07
  • H04J2203/0001—Provisions for broadband connections in integrated services digital network using frames of the Optical Transport Network [OTN] or using synchronous transfer mode [STM], e.g. SONET, SDH
  • H04J2203/0073—Services, e.g. multimedia, GOS, QOS
  • H04J2203/0082—Interaction of SDH with non-ATM protocols
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W88/00—Devices specially adapted for wireless communication networks, e.g. terminals, base stations or access point devices
  • H04W88/08—Access point devices
  • H04W88/085—Access point devices with remote components
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W88/00—Devices specially adapted for wireless communication networks, e.g. terminals, base stations or access point devices
  • H04W88/18—Service support devices; Network management devices
  • H04W88/181—Transcoding devices; Rate adaptation devices
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W92/00—Interfaces specially adapted for wireless communication networks
  • H04W92/16—Interfaces between hierarchically similar devices
  • H04W92/20—Interfaces between hierarchically similar devices between access points

Definitions

• the present invention relates to telecommunications, in particular to wireless telecommunications.
• base band units In many wireless base stations, base band units (BBUs) are separate and physically remote from remote radio-heads (RRHs). In these solutions the radio- frequency front end and the analog-to-digital interface are part of a remote radio-head (RRH).
• An RRH is connected to a base band unit (BBU) via a digital transport network. Digitised base band complex inphase (I) and quadrature phase (Q) samples are transported over the transport network.
• I inphase
• Q quadrature phase
• CPRI Common Public Radio Interface
• a remote radio head is a Radio Equipment (RE) and a base band unit is a Remote Equipment Controller (REC).
• RE Radio Equipment
• REC Remote Equipment Controller
• a known way to connect a remote radio-head (RRH) to a base band unit is to use optical fibres as point-to-point links.
• RRH remote radio-head
• Another known approach is to use optical multiplexing so as to reduce the number of fibres required.
• An example of the present invention is a method of processing a digital signal for transmission comprising digital data frames, by compressing the digital data frames; and generating an optical data unit for transmission comprising multiple of the compressed digital data frames.
• the optical data unit is configured for transport by an Optical Transport Network, OTN.
• Preferred embodiments provide aggregation and concentration of digital radio data at a wireless cell site for transmission via an OTN.
• up to eighteen remote radio-heads are connectable to a base band unit via the OTN.
• the digital data frames are Common Public Radio Interface (CPRI) data frames.
• the digital data frames are compressed and aggregated into up to two 10 Gigabit G.709 frames, namely ODU2, and transmitted through the OTN.
• the OTN may be, for example, a Passive Optical Network (PON), for example a lOGigabit Passive Optical Network (10GPON), a Wave Division Multiplex Passive Optical Network (WDM PON),a WDM overlay to a 10GPON, a CDWM optical ring or a DWDM optical ring.
• PON Passive Optical Network
• 10GPON lOGigabit Passive Optical Network
• WDM PON Wave Division Multiplex Passive Optical Network
• WDM overlay to a 10GPON
• CDWM optical ring CDWM optical ring
• DWDM optical ring DWDM optical ring
• Preferred embodiments provide compression of some radio data flows and aggregating them inside an optical flow to make good use of bandwidth.
• the optical flow can be transmitted through any type of Optical Transport Network (OTN).
• OTN Optical Transport Network
• the number of point to point links and the number of wavelengths used is small.
• Another aspect of the present invention is a method of processing an optical data unit upon reception from an Optical Transport Network, OTN, by splitting the optical data unit into multiple compressed digital data frames; and decompressing each of the compressed digital data frames.
• OTN Optical Transport Network
• a further aspect of the present invention is a network element for a
• the element comprises: a compressor configured to compress digital data frames; a generator configured to generate a first optical data unit for transmission comprising multiple of the compressed digital data frames, the first optical data unit being configured for transport by an Optical Transport Network, OTN; a processor configured to split a second optical data unit upon reception from an Optical Transport Network, OTN, into multiple compressed digital data frames; and a decompressor configured to decompressing each of the compressed digital data frames from the second optical data unit so as to provide digital data frames.
• FIG. 1 is a diagram illustrating a system including remote radio-heads (RRH) and a base band unit (BBU), an Optical Transport Network (OTN), and first and second interface boxes,
• RRH remote radio-heads
• BBU base band unit
• OTN Optical Transport Network
• Figure 2 is a diagram illustrating in more detail the first interface box shown in Figure 1,
• FIG 3 is a diagram illustrating in further detail the first interface box shown in Figure 2
• FIG. 4 is a flow-chart illustrating compression of CPRI formatted radio data
• FIG. 5 is a diagram illustrating multiplexing and encapsulation of the compressed radio data into an optical data unit for transmission over the Optical Transport Network (OTN),
• OTN Optical Transport Network
• Figure 6 is a diagram illustrating in further detail the second interface box shown in Figure 1 .
• Figure 7 is a diagram illustrating the decompression of radio data into CPRI formatted radio data
• Figure 8 is a diagram illustrating an example of switching by the interface boxes shown in Figure 1 (switching is to a single BBU)
• Figure 9 is a diagram illustrating switching by the interface boxes in a second embodiment of the invention
• Figure 10 is a diagram illustrating switching by the interface boxes in a third embodiment of the invention.
• Figure 11 is a diagram illustrating switching by the interface boxes in a fourth embodiment of the invention.
• the example system 2 includes multiple remote radio- heads (RRH) 4, three of which are shown for simplicity, each connected by one or two respective links 3 to a first interface box 6 to an Optical Transport Network (OTN) 8.
• the OTN 8 is also connected to a second interface box 10 which is connected to a base band unit (BBU) 12 by a number of links 7 corresponding to the number of links 3 from the first interface box 6 to the remote radio heads 4.
• BBU base band unit
• the remote radio heads 4 are located at a shared cell site 5.
• Remote radio-head RRH
• Base band Unit BBU
• the remote radio-head does not perform BBU functionality, for example does not perform physical layer processing that is specific to any particular wireless technology. Furthermore, in this example no control signalling is exchanged between the remote radio-heads and base band units.
• each remote radio head 4 one of which is shown for simplicity, includes conventional circuitry.
• the RRH 4 includes a radio-frequency front-end 14 and an analog-to digital converter (ADC) 16 that converts the received analog radio signal into digital I/Q sample form in a known data frame format consistent with the Common Public Radio Interface (CPRI) Standard.
• ADC analog-to digital converter
• CPRI Common Public Radio Interface
• the known CPRI basic frame format is used, illustrated on the left hand side of Figure 3.
• the CPRI frames are provided to the first interface box 6 for data transmission via the OTN 8 and second interface box 10 to the base band unit 12. This is described in more detail later below.
• the BBU 12 includes conventional circuitry namely a transmitter 18 which generates I/Q samples in data frames of CPRI format. These frames are provided to the second interface box 10 for data transmission via the OTN 8 and first interface box 6 to the remote radio-head (RRH) 4.
• the conventional remote radio-head (RRH) includes a digital to analog converter (DAC, not shown in Figure 2, but shown in Figure 6) to convert the signal to radio frequency signals transmitted via antenna 20.
• DAC digital to analog converter
• the RRH radio frequency front end, ADC, DAC and the BBU processing are known, there being nothing in those subsystems implemented to accommodate compression and packing into G709 ODUs for transport over the Optical Transport Network (OTN) nor unpacking and decompression to provide data in CPRI frame format once more.
• OTN Optical Transport Network
• OTN Optical Transport Network
• the Optical Transport Network is one in accordance with the ITU-T Recommendation G.709 standard as at the first filing date of this patent application.
• the OTN is G.709 compliant.
• the OTN may be a Passive Optical Network (PON), for example a Gigabit Passive Optical Network (GPON), Ethernet Passive Optical Network (EPON) or Wave Division Multiplex Passive Optical Network (WDM PON).
• PON Passive Optical Network
• GPON Gigabit Passive Optical Network
• EPON Ethernet Passive Optical Network
• WDM PON Wave Division Multiplex Passive Optical Network
• the OTN may be a Fibre-to-the-x (FTTx) infrastructure.
• FTTx Fibre-to-the-x
• the OTN may be a ring such as a WDM ring, for example a Course Wave Division Multiplexing (CWDM) ring or a Dense Wave Division Multiplexing (DWDM) ring.
• WDM Wideband Wave Division Multiplexing
• DWDM Dense Wave Division Multiplexing
• the OTN may be based on point-to-point (P2P) fibres.
• P2P point-to-point
• OTU2 Optical Transport Unit 2
• ODU2 Optical Data Unit2
• the ODU2 signal is a server layer signal for client signals.
• An ODU2 may transport a stream of packets, such as Ethernet, MPLS, Internet Protocol, or Common Public Radio Interface (CPRI) packets.
• CPRI Common Public Radio Interface
• the interface boxes are bi-directional; however, it will be noted that uplink and downlink processing for transmission by the OTN operate in essentially the same manner. Similarly, uplink and downlink processing upon reception from the OTN operates in essentially the same manner. Accordingly, basically speaking, a single instance of processing for transmission by the OTN (namely uplink) and a single instance of processing upon reception from the OTN (namely uplink) will be described for the sake of brevity.
• Uplink denotes the direction towards the base band unit.
• Downlink denotes the direction towards the RRH.
• the interface box 6 connected to the remote radio-heads (RRH) 4 includes a CPRI compressor/decompressor 20 which, in this example, may be considered to consist of an uplink compressor 22 and a downlink decompressor 24.
• the uplink compressor 22 is connected to the ADC 16 of the RRH 4.
• the downlink decompressor 24 is connected to the DAC 18 of the RRH 4.
• the compressor 22 and decompressor 24 are connected to a switch 26 which is connected to a multiplexer/demultiplexer (MUX/DEMUX) 28 which is connected to a G.709 converter 30.
• MUX/DEMUX multiplexer/demultiplexer
• FIG. 3 show the interface box 6 in more detail.
• CPRI frames 34 are input via twelve CPRI input links 3 into the CPRI compressor/decompressor 20.
• compressor/decompressor 20 and a switch 26 that has twelve links to the
• each remote radio head 4 provides one or two CPRI links to the first interface box 6.
• CPRI links For completeness, we mention here that various numbers of CPRI links are envisaged. In another embodiment, for example, eighteen links are provided used by multiple radio heads that each use one or two of the CPRI links.
• radio heads may be connected to an interface box using different numbers of CPRI links, and/or different numbers of remote radio heads may be connected to the interface box.
• more than one remote radio head may be connected to a CPRI link, for example by being daisy-chained.
• the switch 26 and MUX/DEMUX 28 act to control to which Optical Data Unit ODU2 the CPRI frames are directed.
• Figure 4 is a flow chart showing the compression that occurs in compressor 22 for example). As shown, the compression involves three main processes, namely removal of redundancies in the spectral domain S500, block scaling S510 and quantization S520. Each process will be described in detail below.
• the sampling rate of the ADC, DAC and BBU processing is higher than the minimum required according to the Nyquist sampling theorem.
• the sampling rate is 15.36 MHz (both for the BBU processing and in the case of CPRI uncompressed transmission).
• 2-time and 4-time oversampling is customary. This results in redundancies in the spectral or frequency domain. Namely, in the uncompressed form, a spectrally broader signal is transmitted than what may be necessary.
• the removal process includes low-pass filtering S502 the digital base band signal followed by decimation S504.
• these processes are performed in a streaming fashion, sample-by-sample.
• the filtering S502 is performed by a finite-impulse response (FIR) filter
• decimation S504 is performed by up- and down-sampling.
• the filtering S502 and decimation S504 will depend on the base band signal, and particularly, the frequency band and amount of oversampling.
• LTE Long Term Evolution
• bandwidth and sampling rate are specified for a given wireless technology.
• the low-pass filter parameters are selected empirically or by design choice to balance and/or optimize complexity- versus-performance tradeoff.
• Block scaling may also be called block floating-point.
• a block of K I/Q samples output from the decimation operation S504 are collected in step S512.
• the block of K I/Q samples are then divided by a scaling factor in step S514.
• the scaling factor may be a fixed number of bits, the value of which may vary block-by-block.
• block scaling is performed on a 24-sample block, with 16 bits used to represent the scaling factor.
• the corresponding corresponding scaling factor may be determined as shown by the equation below (where Nb denotes bit-resolution):
• Each sample in the block is then multiplied by the above scaling factor.
• This equation may also be used to determine the scaling factor in any of the described embodiments.
• the block length K is a design parameter and may be derived from a trade-off analysis between desired signal quality (e.g., EVM and ACPR) and transport data rates.
• desired signal quality e.g., EVM and ACPR
• the block length K may be fixed. However, as will be discussed in greater detail below. The block length is not limited to being fixed.
• the block length may be dynamically and/or adaptively determined.
• scaling factor may change, one or more of these parameters may be transmitted adding to overhead.
• the scaling factor may be transmitted once every K I/Q samples. Lowering the block length K will lower the subsequent quantization error, while increasing the scaling factor
• the block length K is a design parameter derived from the trade-off analysis between the required signal quality and transport data rates.
• I/Q samples are quantized using a quantizer with N ⁇ -bit resolution per each complex component.
• N the number of bits representing a sample is truncated to the Nb most significant bits. This operation is performed sample-by-sample.
• a simple linear (i.e., uniform) quantizer may be applied.
• the resolution Nb is a design parameter derived from the trade-off analysis between the required signal quality and data rates.
• the switch 26 acts to direct the compressed CPRI frames.
• the MUX DEMUX 28 acts to multiplex multiple Compressed CPRI frames into shared channels so that there are fewer outputs than inputs, and less bandwidth is used for transmission in consequence (in other words, less "lambda").
• G.709 encapsulation so as to provide an ODU2 frame.
• the ODU2 frame includes ODU2 overhead and Optical Channel Payload Unit
• OTU2 Optical Transport Unit
• OAM Operations &Management
• the OTU2 frames are transported over the Optical Transport Network (OTN) 8 and received by the second interface box 10.
• the second interface box includes a G.709 converter 30' connected to a MUX/DEMUX 28' which is connected to a switch 26'.
• the switch is connected to an uplink decompressor 20' and a downlink compressor 22' of a CPRI compressor/decompressor 20'.
• This second interface box 10 essentially acts in this uplink direction to reverse the processing steps undertaken in the first interface box 6.
• the G.709 converter 30' acts to de-encapsulate the concatenated compressed CPRI data by removing OTU2 and ODU2 headers, FEC etc.
• the resulting data stream is then demultiplexed in the MUX/DEMUX 28' to provide the compressed CPRI frames.
• the switch 26' then sends the compressed CPRI frames to the uplink decompressor 22'.
• decompression involves three main processes:
• dequantization S600 dequantization S600
• descaling S610 descaling S610
• insertion of redundancies S620 i.e., up- sampling.
• the inverse of the quantization operation is performed. Namely, the number of bits used to represent a sample is increased to the same resolution prior to quantization in step S520. In this embodiment, this is performed by adding zeros as least significant bits.
• the inverse of the quantization process conducted in step S520 may be performed.
• the inverse of the pseudo code (A) shown below may be performed if quantization in Step S520 proceeds as set forth in pseudo code (A).
• a block of K samples from the dequantization S600 are collected and multiplied by the scaling factor.
• each sample from the descaling S610 undergoes inverse decimation S622, which is the inverse of the decimation in step S504.
• the resulting samples are inverse filtered in S624, where the
• filtering is the inverse of the filtering performed in step S502. This is an up- sampling procedure.
• the decompressed CPRI frames are then passed to the conventional base band unit 12 via a corresponding number of CPRI links as between the remote radio heads 4 and first interface box 6.
• the receive base-band processing i.e. physical layer processing is undertaken.
• the interface box 6 at the remote radio head side each include Ethernet ports (not shown). These eternet ports are used to tunnel Ethernet data flow between the radio head side and the base band unit side, for example backhauling information or data collected on the radio head side. For example, this information is tunnelled by the interface box 6, either inside the OAM channel (control channels GCC1 or GCC2 of the Optical Data Unit ODU2) or multiplexed with the CPRI data inside the ODU2 payload, so as to be made available to the interface box 10 at the base band unit 12 side.
• the interface box 10 also has Ethernet ports (not shown) which are used to connect to the base band unit 12 for control purposes.
• the interface boxes are bi-directional; however, it will be noted that uplink and downlink processing for transmission by the OTN operate in essentially the same manner. Similarly, uplink and downlink processing upon reception from the OTN operates in essentially the same manner. Accordingly, basically speaking, a single instance of processing for transmission by the OTN (namely uplink) and a single instance of processing upon reception from the OTN (namely uplink) has been described above for the sake of brevity.
• a single first interface box 6 is connected to remote radio heads 4 of one cell site 5 and a single second interface box 10 is connected to a single base band unit 12 (this is illustrated in Figure 8).
• a single base band unit 12 this is illustrated in Figure 8.
• alternatives are possible, for example as follows:
• the second interface box 10' is connected so that some of its outputs are to the base band unit 12' and others of its outputs are to a second base band unit 12a. This allows multiple base band units to be involved, readily expanding base band unit capacity.
• two first interface boxes 6, 6a connect two sets of remote radio-heads (RRH) 4a, 4b from different cell sites 5a, 5b to the OTN 8' and two second interface boxes 10a, 10b both connect to a base band unit 12".
• the allocation of CPRI links to the base band unit 12" is static but the base band unit 12" is shared by both the first interface box 6a to second interface box 10a system, and the first interface box 6b to second interface box 10b system.
• Appropriate allocation of CPRI links to base band units requires knowledge of the statistical distribution of traffic and of the number of remote radio heads to be served.
• a second base band unit 12b is shared between the two sets of remote radio-heads (RRH) 4a', 4b' from different cell sites 5a', 5b' according to the time of day. From 7am to 7pm (daytime), selected CPRI links H,I,J from a first remote radio-head (RRH) 4a' go to a second base band unit BBU#2 via the OTN whilst other selected CPRI links A,B,C from the first remote radio-head (RRH) 4a' go to the first BBU#1.
• two or more first interface boxes can be used to connect two or more remote radio heads, via the Optical Transport Network and a single second interface box, to a single base band unit.
• an interface box receiving the ODU2 can switch its outputs for fault management purposes, for example to avoid sending digital date frames to a known- to-be-faulty base band unit.
• OBSAI Open Base Station Architecture Initiative
• ORI Open Radio Initiative
• the example embodiments are applicable to different wireless technologies, for example 3 GPP (Third Generation Partnership Project) Long Term Evolution (LTE), LTE-Advanced, Universal Mobile Telecommunications System (UMTS) such as High Speed Packet Access (HSPA), as well as on the uplink and downlink.
• 3 GPP Three Generation Partnership Project
• LTE Long Term Evolution
• UMTS Universal Mobile Telecommunications System
• High Speed Packet Access HSPA
• program storage devices e.g., digital data storage media, which are machine or computer readable and encode machine-executable or computer-executable programs of instructions, wherein said instructions perform some or all of the steps of said above-described methods.
• the program storage devices may be, e.g., digital memories, magnetic storage media such as a magnetic disks and magnetic tapes, hard drives, or optically readable digital data storage media.
• Some embodiments involve computers programmed to perform said steps of the above-described methods.

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• 2011
  • 2011-12-05 EP EP11290558.3A patent/EP2602948A1/en not_active Ceased
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