Pre-start-up procedure for internal interface of distributed radio base station

0001This application claims the benefit and priority of the following U.S. Provisional Patent Applications, all of which are incorporated herein by reference: (1) U.S. Provisional Application 60/520,323, entitled “Encapsulation of Diverse Protocols Over Internal Interface of Distributed Radio Base Station”; (2) U.S. patent application Ser. No. 60/520,324, entitled “Encapsulation of Independent Transmissions Over Internal Interface of Distributed Radio Base Station”; (3) U.S. patent application Ser. No. 60/520,364, entitled “Interface, Apparatus, and Method for Cascaded Radio Units In A Main-Remote Radio Base Station”; and, (4) U.S. patent application Ser. No. 60/520,325, entitled “Pre-Start-Up Procedure For Internal Interface of Distributed Radio Base Station”. This application is related to the following simultaneously filed U.S. patent applications, all of which are incorporated by reference herein in their entirety: (1) U.S. patent application Ser. No. ______, entitled “Encapsulation of Diverse Protocols Over Internal Interface of Distributed Radio Base Station” (attorney docket: 2380-834); and (2) U.S. patent application Ser. No. ______, entitled “Pre-Start-Up Procedure For Internal Interface of Distributed Radio Base Station” (attorney docket: 2380-836).

BACKGROUND

00021. Field of the Invention

0003This application is related to radio access networks involved in wireless telecommunications, and particularly relates to an internal interface (such as the Common Public Radio Interface (CPRI)) of a radio base station which links a radio equipment portion of the radio base station to a radio equipment control portion of the base station.

00042. Related Art and Other Considerations

0005In a typical cellular radio system, wireless user equipment units (UEs) communicate via a radio access network (RAN) to one or more core networks. The user equipment units (UEs) can be mobile stations such as mobile telephones (“cellular” telephones) and laptops with mobile termination, and thus can be, for example, portable, pocket, hand-held, computer-included, or car-mounted mobile devices which communicate voice and/or data with radio access network. Alternatively, the wireless user equipment units can be fixed wireless devices, e.g., fixed cellular devices/terminals which are part of a wireless local loop or the like.

0006The radio access network (RAN) covers a geographical area which is divided into cell areas, with each cell area being served by a radio base station. A cell is a geographical area where radio coverage is provided by the radio equipment at a base station site. Each cell is identified by a unique identity, which is broadcast in the cell. The radio base stations communicate over the air interface (e.g., radio frequencies) with the user equipment units (UE) within range of the base stations. In the radio access network, several base stations are typically connected (e.g., by landlines or microwave) to a control node known as a base station controller (BSC) or radio network controller (RNC). The control node supervises and coordinates various activities of the plural radio base stations connected thereto. The radio network controllers are typically connected to one or more core networks.

0007One example of a radio access network is the Universal Mobile Telecommunications (UMTS) Terrestrial Radio Access Network (UTRAN). The UMTS is a third generation system which, at least in some respects, builds upon the radio access technology known as Global System for Mobile communications (GSM) developed in Europe. UTRAN is essentially a radio access network providing wideband code division multiple access (WCDMA) to user equipment units (UEs).

0008In many radio access networks the radio base station is a concentrated node with essentially most of the components being located at concentrated site. In the future mobile network operators may be afforded more flexibility if the radio base station is configured with a more distributed architecture. For example, a distributed radio base station can take the form of one or more radio equipment portions that are linked to a radio equipment control portion over a radio base station internal interface.

0009One example of an internal interface of a radio base station which links a radio equipment portion of the radio base station to a radio equipment control portion of the base station is the Common Public Radio Interface (CPRI). The Common Public Radio Interface (CPRI) is described in Common Public Radio Interface Specification Version 1.0 (Sep. 26, 2003) and Version 1.1 (May 10, 2004), and which are incorporated by reference herein in their entirety.

0010The Common Public Radio Interface Specification Version 1.0 (Sep. 26, 2003) and Version 1.1 (May 10, 2004) describe a standardized start-up procedure which is supposed to accomplish two main objectives. The first objective is synchronization of the physical layer (layer <b>1</b>), e.g., byte alignment and hyperframe alignment. The second objective is to align the capabilities of the radio equipment controller (REC) and the radio equipment (RE), particularly with respect to line bit rate, C&amp;M (control and maintenance) link speed, C&amp;M protocol, and vendor specific signaling. According to the specification, since there is no mandatory line bit rate of C&amp;M link speed, the radio equipment controller (REC) and radio equipment (RE) must, during the start-up procedure, try different configurations until a common match is detected.

0011<figref idref="DRAWINGS">FIG. 11</figref> illustrates the start-up states and transitions for the standardized start-up procedure discussed in the Common Public Radio Interface Specification Version 1.0 (Sep. 26, 2003) and Version 1.1 (May 10, 2004). <figref idref="DRAWINGS">FIG. 11</figref> shows start-up states A through F, and sixteen possible transitions into or between states A through F. These states and transitions are applicable to each of the radio equipment controller (REC) portion and the radio equipment (RE) portion of the radio base station (RBS).

0012In state A, the RBS portion waits to be configured to start-up the internal interface, there thus far being no reception or transmission on the internal interface. In conjunction with state A, the Common Public Radio Interface Specification Version 1.0 (Sep. 26, 2003) and Version 1.1 (May 10, 2004) mention that the operator may configure a suitable start-up configuration (e.g., line bit rate, C&amp;M link characteristics), and that the radio equipment controller (REC) and radio equipment (RE) may also have knowledge about a previous successful configuration.

0013In state B, an “available set” of line bit rate, protocol revisions, and C&amp;M plane characteristics are known. According to the standard, this may be the complete set of the unit or a subset based on operator configuration or previous negotiation between the units (e.g., from state E). In state B the line bit rate of the interface is determined and both the radio equipment controller (REC) and the radio equipment (RE) reach a certain layer <b>1</b> synchronization.

0014The Common Public Radio Interface Specification Version 1.0 (Sep. 26, 2003) and Version 1.1 (May 10, 2004) state that the transition <b>1</b> from state A to state B is out of the scope of the specification, indicating that a set of available line bit rates, protocol revisions, and C&amp;M link bit rates shall be available (the “available set”). The specification states that this may be the equipment full capabilities or a subset determined by the equipment configuration (manual) or knowledge from previous successful configurations.

0015The Common Public Radio Interface Specification Version 1.0 (Sep. 26, 2003) and Version 1.1 (May 10, 2004) further prescribe a layer <b>1</b> start-up timer. If the layer <b>2</b> start-up timer expires, transition <b>16</b> takes place and state B is entered, possibly modifying the available set of line bit rates and protocols.

0016Thus, Common Public Radio Interface Specification Version 1.0 (Sep. 26, 2003) and Version 1.1 (May 10, 2004) specify a standard start-up procedure with automatic negotiation of an “available set” of protocol and line bit rate. The standard start-up procedure as shown in <figref idref="DRAWINGS">FIG. 11</figref> can be viewed as an “inner loop”. The standard start-up procedure requires an “outer loop” of operations which is to provide the “available set” for the “inner loop” to use for negotiation. This “outer loop”, which provides the “available set” for use in inner loop negotiations, is outside the specification.

0017The standard start-up procedure as prescribed by the Common Public Radio Interface Specification Version 1.0 (Sep. 26, 2003) and Version 1.1 (May 10, 2004) have some disadvantages. As a first disadvantage, the standard start-up procedure takes a long time if there are many line bit rates. As a second disadvantage, the standard start-up procedure can hang if the negotiation agrees upon a line bit rate and protocol for which no common C&amp;M links are supported. A third disadvantage is that, when a line bit rate change is required, such a change must be executed very quickly, thereby imposing difficult requirements on the hardware.

0018What is needed therefore, and an object of the present invention, is a technique for supplying an available set of line bit rate and protocol to a start-up procedure for an internal interface of a distributed radio base station.

BRIEF SUMMARY

0019A radio base station has an internal interface connecting a radio equipment (RE) and a radio equipment controller (REC). The radio base station performs a pre-start-up procedure or method for the internal interface. The pre-start-up procedure is preformed preparatory to and/or in conjunction with a start-up procedure for the internal interface. The start-up procedure for the internal interface serves to synchronize a physical layer and align line bit rate and protocol over the internal interface. In one example implementation, the internal interface is a Common Public Radio Interface (CPRI).

0020As one of its aspects, the pre-start-up procedure involves storing one or more previously proven combinations of line bit rate and protocol as stored combination(s) for use on the internal interface. Prior to synchronization of the internal interface, the stored combination(s) are retrieved and included in a temporary available set of combinations of line bit rate and protocol. Thereafter the start-up procedure for the internal interface is initiated for the purpose of determining efficacy of the temporary available set.

0021Should synchronization of the physical layer by the start-up procedure succeed, the pre-start-up procedure uses a valid combination of line bit rate and protocol in the available set for negotiating between the radio equipment controller (REC) and the radio equipment (RE). A best combination of line bit rate and protocol is determined during the negotiating. Should the valid combination be agreed to be the best combination during the negotiating, the start-up procedure is end and an operational state entered. On the other hand, should the valid combination not be the best combination, only the best combination of line bit rate and protocol is included in the available set, and thereafter the start-up procedure is restarted. At various junctures the temporary active set is set to be the valid combination of line bit rate and protocol in order to expedite processing should the start-up procedure fail.

0022In another of its aspects, the pre-start-up procedure classifies the temporary available set into plural subsets, each subset of the temporary available set containing combinations of line bit rate and protocol having a same line bit rate. The pre-start-up procedure separately initiates the start-up procedure for the internal interface for each subset. The pre-start-up procedure can sequence in a predefined or preferred order the use of the subsets in the initiations of the start-up procedure. Since switching between different line bit rates takes time, this aspect of the pre-start-up procedure simplifies hardware design.

0023In another of its aspects, the pre-start-up procedure classifies the stored combinations as: (1) a best last time combination of line bit rate and protocol which was involved in a last successful execution of the start-up procedure; and (2) a union all combinations of line bit rate and protocol for which the synchronization of the physical layer has previously been successful during the start-up procedure. Capitalizing upon this classification, the pre-start-up procedure can use the best last time combination as the temporary available set for initiating the start-up procedure for the internal interface. Then, if the start-up procedure fails, the pre-start-up procedure can resort to using the union of all combinations as the temporary available set for initiating the start-up procedure for the internal interface.

0024In another of its aspects, after the pre-start-up procedure has initiated the start-up procedure for the internal interface to determine efficacy of a set of combinations of line bit rate and protocol, the pre-start-up procedure removes a failed combination of line bit rate and protocol from the set should the start-up procedure fail.

0025In example embodiments, the pre-start-up procedure is performed by a controller which can take the form of a processor or of a dedicated logic part (e.g., part of an ASIC).

BRIEF DESCRIPTION OF THE DRAWINGS

0026<figref idref="DRAWINGS">FIG. 1</figref> is a schematic view of an example embodiment of a distributed radio base station.

0027<figref idref="DRAWINGS">FIG. 2</figref> is a diagrammatic view of a protocol overview for an interface between radio equipment controller (REC) <b>22</b> and a radio equipment (RE) <b>24</b>.

0028<figref idref="DRAWINGS">FIG. 3A</figref> is a diagrammatic view of basic frame structure for one example data rate for use over an internal interface for the distributed base station.

0029<figref idref="DRAWINGS">FIG. 3B</figref> is a diagrammatic view of a hyperframe structure for one example implementation.

0030<figref idref="DRAWINGS">FIG. 3C</figref> is an enlargement of a portion of <figref idref="DRAWINGS">FIG. 3B</figref>.

0031<figref idref="DRAWINGS">FIG. 4</figref> is a schematic view of selected aspects of an example radio equipment (RE) portion of the distributed radio base station of <figref idref="DRAWINGS">FIG. 4</figref>.

0032<figref idref="DRAWINGS">FIG. 5</figref> is a schematic view of selected aspects of a radio equipment controller (REC) portion of the distributed radio base station of <figref idref="DRAWINGS">FIG. 4</figref>.

0033<figref idref="DRAWINGS">FIG. 6</figref> is a diagrammatic view showing selected basic states of an example mode of a pre-start-up procedure performed by a distributed radio base station.

0034<figref idref="DRAWINGS">FIG. 7</figref> is a diagrammatic view showing optional further actions that can be performed in the example pre-start-up procedure shown in <figref idref="DRAWINGS">FIG. 6</figref>.

0035<figref idref="DRAWINGS">FIG. 8</figref> is a schematic view of selected aspects of apparatus for performing the pre-start-up procedure of <figref idref="DRAWINGS">FIG. 6</figref>.

0036<figref idref="DRAWINGS">FIG. 9</figref> is a flowchart showing a mode of a pre-start-up procedure which classifies and selectively uses combinations.

0037<figref idref="DRAWINGS">FIG. 10A</figref> is a diagrammatic view showing several internal interface physical links connecting a radio equipment controller (REC) and a radio equipment (RE).

0038<figref idref="DRAWINGS">FIG. 10B</figref> is a diagrammatic view showing several radio equipment entities (RE) being served by one radio equipment controller (REC).

0039<figref idref="DRAWINGS">FIG. 11</figref> is a diagrammatic view showing states of an example standard start-up procedure in conjunction with which the pre-start-up procedure of <figref idref="DRAWINGS">FIG. 6</figref> operates.

DETAILED DESCRIPTION

0040In the following description, for purposes of explanation and not limitation, specific details are set forth such as particular architectures, interfaces, techniques, etc. in order to provide a thorough understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced in other embodiments that depart from these specific details. In other instances, detailed descriptions of well-known devices, circuits, and methods are omitted so as not to obscure the description of the present invention with unnecessary detail. Moreover, individual function blocks are shown in some of the figures. Those skilled in the art will appreciate that the functions may be implemented using individual hardware circuits, using software functioning in conjunction with a suitably programmed digital microprocessor or general purpose computer, using an application specific integrated circuit (ASIC), and/or using one or more digital signal processors (DSPs).

0041<figref idref="DRAWINGS">FIG. 1</figref> shows an example embodiment of a distributed radio base station <b>20</b>. The radio base station <b>20</b> comprises both a radio equipment controller (REC) <b>22</b> and a radio equipment (RE) <b>24</b>. The radio equipment controller (REC) <b>22</b> and radio equipment (RE) <b>24</b> are connected by an internal interface <b>26</b>. In the example implementation herein described, internal interface <b>26</b> is a CPRI link. Details of structure and operation of radio base station <b>20</b> and an internal interface <b>26</b> which takes the form of a CPRI link are understood from the Common Public Radio Interface Specification Version 1.0 (Sep. 26, 2003) and Version 1.1 (May 10, 2004), which are incorporated by reference herein in their entirety. As in the specification, the description herein is based on the UMTS (Universal Mobile Telecommunication System) nomenclature. However, the radio base station <b>20</b> and the internal interface <b>26</b> may operate in accordance with other radio standards.

0042The radio equipment controller (REC) <b>22</b> and radio equipment (RE) <b>24</b> may be physically separated (i.e., the radio equipment (RE) <b>24</b> may be close to the antenna, whereas the radio equipment controller (REC) <b>22</b> may be located in a conveniently accessible site). Alternatively, both radio equipment controller (REC) <b>22</b> and radio equipment (RE) <b>24</b> may be co-located as in a conventional radio base station design. Whatever the distance therebetween, in view of their physical separation the location of the radio equipment controller (REC) <b>22</b> is known as the main site and the location of the radio equipment (RE) <b>24</b> is known as the remote site.

0043As illustrated in <figref idref="DRAWINGS">FIG. 1</figref>, radio equipment controller (REC) <b>22</b> provides an access towards an unillustrated Radio Network Controller via the lub interface <b>30</b> (for the UMTS radio access network). Basically, the radio equipment controller (REC) <b>22</b> is concerned with the Iub transport and lub protocols, the Node B (base station) control and management, as well as the digital baseband processing. For the downlink (i.e., from radio equipment controller (REC) <b>22</b> to radio equipment (RE) <b>24</b>), the radio equipment controller (REC) <b>22</b> handles such operations as channel coding, interleaving, spreading, scrambling, adding of physical channels, controlling transmit power of each physical channel, frame and slot signal generation (including clock stabilization). For the uplink (i.e., from radio equipment (RE) <b>24</b> to radio equipment controller (REC) <b>22</b>), the radio equipment controller (REC) <b>22</b> handles such operations as channel de-coding, de-interleaving, de-spreading, de-scrambling, signal distribution to signal processing units, detection of feedback information for transmit power control, and signal to interference ratio measurement.

0044The radio equipment (RE) <b>24</b> serves the air interface <b>32</b> to the user equipment (in an UMTS network the air interface is called the Uu interface). The user equipment unit, or mobile station, is not illustrated in <figref idref="DRAWINGS">FIG. 1</figref>. The radio equipment (RE) <b>24</b> provides the analogue and radio frequency functions such as filtering, modulation, frequency conversion and amplification. For the downlink, the radio equipment (RE) <b>24</b> performs operations such as digital to analogue conversion, up conversion, on/off control of each carrier, carrier multiplexing, power amplification and limiting, antenna supervision, and RF filtering. For the uplink, the radio equipment (RE) <b>24</b> performs operations such as analogue to digital conversion, down conversion, automatic gain control, carrier de-multiplexing, low noise amplification, and RF filtering.

0045Thus, the radio equipment controller (REC) <b>22</b> comprises the radio functions of the digital baseband domain, whereas the radio equipment (RE) <b>24</b> contains the analogue radio frequency functions. The functional split between both parts is done in such a way that a generic interface based on In-Phase and Quadrature (IQ) data can be defined.

0046The Common Public Radio Interface Specification Version 1.0 (Sep. 26, 2003) and Version 1.1 (May 10, 2004) define protocols for the physical layer <b>34</b> (layer <b>1</b>) and the data link layer <b>36</b> (layer <b>2</b>). Layer <b>1</b> defines, e.g., electrical characteristics, optical characteristics, time division multiplexing of the different data flows, and low level signaling. Layer <b>2</b> defines the media access control, flow control and data protection of the control and management information flow.

0047The Common Public Radio Interface Specification Version 1.0 (Sep. 26, 2003) and Version 1.1 (May 10, 2004) further describe four protocol data planes: control plane, management plane, user plane, and synchronization. These four protocol data planes are illustrated in <figref idref="DRAWINGS">FIG. 2</figref>.

0048The control plane involves control data flow used for call processing. The management plane carries management information for the operation, administration and maintenance of the CPRI link and the radio equipment (RE) <b>24</b>. The control and management data is exchanged between control and management entities with the radio equipment controller (REC) <b>22</b> and radio equipment (RE) <b>24</b>, and is given to higher protocol layers. The control and management plane is mapped to a single information flow over the CPRI link.

0049The user plane concerns data that has to be transferred from the radio base station to the mobile station and vice versa. The user plane data is transported in the form of in-phase and quadrature (IQ) modulation data (digital base band signals), represented by block <b>40</b> in <figref idref="DRAWINGS">FIG. 2</figref>. Several IQ data flows will be sent via one physical CPRI link <b>26</b>. Each IQ data flow reflects the data of one antenna for one carrier, the so-called antenna-carrier (AxC). In general, without regard to specific protocol, one antenna-carrier is the amount of digital baseband (IQ) U-plane data necessary for either reception of transmission of one carrier at one independent antenna element. An AxC container contains the IQ samples of one AxC for one UMTS chip duration. Each flow in the user plane has reserved a certain bit field per frame, denoted as the AxC carrier. When the internal interface <b>26</b> is a CPRI interface, the AxC container contains samples of a chip an a UTRA-FDD carrier.

0050Synchronization pertains to data flow which transfers synchronization and timing information between radio equipment controller (REC) <b>22</b> and radio equipment (RE) <b>24</b>. Synchronization data is used for alignment of the <b>8</b>B/<b>10</b>B coder as well as the detection of chip, hyperframe, radio frame boundaries, and associated frame numbering.

0051Inband signaling, depicted by block <b>42</b> in <figref idref="DRAWINGS">FIG. 2</figref>, is signaling information that is related to the link and is directly transported by the physical layer. This information is required, e.g. for system startup, layer <b>1</b> link maintenance and the transfer of time critical information that has a direct time relationship to layer <b>1</b> user data.

0052Block <b>44</b> of <figref idref="DRAWINGS">FIG. 2</figref> shows vendor specific information, i.e., an information <b>10</b> flow which is reserved for vendor specific information. This vendor specific information area typically has about 50 Mbps free bandwidth.

0053There are service access points (SAP) for all protocol data plane layer <b>2</b> services which are used as reference points for performance measurements. As illustrated in <figref idref="DRAWINGS">FIG. 1</figref>, for both radio equipment controller (REC) <b>22</b> and radio equipment (RE) <b>24</b> there are service access points SAPCM, SAPS, and SAPIQ for the control &amp; management planes, the synchronization plane, and the user plane, respectively.

0054Thus, in addition to the user plane data (IQ data), control and management as well as synchronization signals have to be exchanged between radio equipment controller (REC) <b>22</b> and radio equipment (RE) <b>24</b>. All information streams are multiplexed onto a digital serial communication line using appropriate layer <b>1</b> and layer <b>2</b> protocols. The different information flows have access to the layer <b>2</b> via the appropriate service access points (SAPs). These information streams define the common public radio interface.

0055The IQ data of different antenna carriers are multiplexed by a time division multiplexing scheme onto an electrical or optical transmission line forming the internal interface <b>26</b>. The Control and Management data are either sent as inband signalling (for time critical signalling data) or by layer <b>3</b> protocols (not defined by Common Public Radio Interface Specification Version 1.0 (Sep. 26, 2003) and Version 1.1 (May 10, 2004)) that reside on top of appropriate layer <b>2</b> protocols. Two different layer <b>2</b> protocols—High Data Level Link Control (HDLC) and Ethernet, depicted as <b>46</b> and <b>48</b>, respectively, in <figref idref="DRAWINGS">FIG. 2</figref>—are supported by CPRI. These additional control and management data are time multiplexed with the IQ data. Finally, additional time slots are available for the transfer of any type of vendor specific information (block <b>42</b>).

0056Information flow over the internal interface <b>26</b> of radio base station <b>20</b> is carried in frames. In the example implementation which is compatible with Common Public Radio Interface Specification Version 1.0 (Sep. 26, 2003) and Version 1.1 (May 10, 2004), the length of a basic frame is 1 Tchip=1/3.84 MHz=260.416667 ns. As shown in <figref idref="DRAWINGS">FIG. 3A</figref>, for such compatible implementation a basic frame consists of 16 words with index W=0 . . . 15. The word with the index W=0, {fraction (1/16)} of the basic frame, is used for one control word. The length T of the word depends on the total data rate. The Common Public Radio Interface Specification Version 1.0 (Sep. 26, 2003) and Version 1.1 (May 10, 2004) define three alternative data rates, each with differing word lengths: 614.4 Mbit/s (length of word T=8); 1228.8 Mbit/s (length of word T=16); and 2457.6 Mbit/s (length of word T=32). <figref idref="DRAWINGS">FIG. 3A</figref> illustrates the frame structure for the 614.4 Mbit/s total data rate.

0057The Common Public Radio Interface Specification Version 1.0 (Sep. 26, 2003) and Version 1.1 (May 10, 2004) also define a hyperframe structure which is hierarchically embedded between the basic frame and the UMTS radio frame as shown in <figref idref="DRAWINGS">FIG. 3B</figref>. In <figref idref="DRAWINGS">FIG. 3B</figref>, Z in the hyperframe number; X is the basic frame number within a hyperframe; W is the word number within a basic frame; and Y is the byte number within a word. The control word is defined as word with rank W=0. Each bit within a word can be addressed with the index B, where B=0 is the LSB of the BYTE Y=0, B=8 is the LSB of BYTE Y=1, B=16 is the LSB of BYTE Y=2, and B=24 is the LSB of BYTE Y=3.

0058<figref idref="DRAWINGS">FIG. 4</figref> shows pertinent basic aspects of an example radio equipment (RE) <b>24</b> as comprising a framer <b>50</b> which is ultimately connected to internal interface <b>26</b>, i.e., the CPRI interface. The framer <b>50</b> works in conjunction with a CPU or processor <b>52</b> of radio equipment (RE) <b>24</b>. The processor <b>52</b> executes control software (SW) <b>54</b> which governs operation, e.g., of framer <b>50</b> and terminates the application layer communication towards the radio equipment controller (REC) <b>22</b>. In addition, radio equipment (RE) <b>24</b> comprises plural transmitters (such as transmitter <b>60</b>₁and transmitter <b>60</b>_a), and plural receivers (such as receiver <b>62</b>₁and receiver <b>62</b>_b). The transmitters <b>60</b> and receivers <b>62</b> can be either single-standard or multistandard. Each transmitter <b>60</b> and each receiver <b>62</b> is connected to a corresponding antenna <b>64</b> (which is distinct from and does not comprise radio equipment (RE) <b>24</b>). The framer <b>50</b> is connected to forward payload information obtained from internal interface <b>26</b> to each of the transmitters <b>60</b> (as shown by lines terminated with solid arrowheads), and to receive information from each of the receivers <b>62</b> to be forwarded from radio equipment (RE) <b>24</b> over the internal interface <b>26</b> to radio equipment controller (REC) <b>22</b> (again as indicated by lines terminated with solid arrowheads, but having a reverse direction toward rather than away from framer <b>50</b>). The processor <b>52</b> is connected to send control information or control signals to each of framer <b>50</b>, the transmitters <b>60</b>, and the receivers <b>62</b>, as shown by lines terminated with non-solid arrowheads).

0059<figref idref="DRAWINGS">FIG. 5</figref> shows pertinent basic aspects of an example radio equipment controller (REC) <b>22</b> as comprising a framer <b>70</b> which is ultimately connected to internal interface <b>26</b>, i.e., the CPRI interface. The framer <b>70</b>. works in conjunction with a CPU or processor <b>72</b> of radio equipment controller (REC) <b>22</b>. The processor <b>72</b> executes control software (SW) <b>74</b> which governs operation, e.g., of framer <b>70</b>. In addition, radio equipment controller (REC) <b>22</b> comprises signal processing units collectively indicated as <b>76</b> in <figref idref="DRAWINGS">FIG. 5</figref>. The radio equipment controller (REC) <b>22</b> of <figref idref="DRAWINGS">FIG. 5</figref> is shown as handling antenna carriers (AxC) AxC <b>1</b> and AxC c on the downlink (DL), and antenna carriers (AxC) AxC <b>1</b> and AxC d on the uplink (UL).

0060The radio base station <b>20</b> performs a pre-start-up procedure or method for the internal interface <b>26</b>. <figref idref="DRAWINGS">FIG. 6</figref> shows selected basic states of an example mode of the pre-start-up procedure performed by a distributed radio base station. The pre-start-up procedure is preformed preparatory to and/or in conjunction with a start-up procedure for the internal interface. As explained previously with respect to <figref idref="DRAWINGS">FIG. 11</figref>, the start-up procedure for the internal interface <b>26</b> serves to synchronize a physical layer and align line bit rate and protocol over the internal interface. In one example implementation, the internal interface <b>26</b> is a Common Public Radio Interface (CPRI).

0061<figref idref="DRAWINGS">FIG. 8</figref> shows other selected aspects of a portion of the distributed radio base station which are pertinent to the pre-start-up procedure herein described. The distributed radio base station portion shown in <figref idref="DRAWINGS">FIG. 8</figref> can be either the radio equipment controller (REC) <b>22</b> or the radio equipment (RE) <b>24</b>. The base station portion shown in <figref idref="DRAWINGS">FIG. 8</figref> comprises a framer F and a processor P. As understood in terms of previously described <figref idref="DRAWINGS">FIG. 4</figref> and <figref idref="DRAWINGS">FIG. 5</figref>, the framer F can be either framer <b>50</b> of radio equipment (RE) <b>24</b> or framer <b>70</b> of radio equipment controller (REC) <b>22</b>, depending on whether the base station portion being illustrated is the radio equipment (RE) <b>24</b> or the radio equipment controller (REC) <b>22</b>. Likewise, the processor P of the base station portion can be processor <b>52</b> of radio equipment (RE) <b>24</b> or processor <b>72</b> of radio equipment controller (REC) <b>22</b>.

0062A control link which includes the service access point for the control and management connects the processor P and framer F. The service access point SAPIQ for the user plane information flow and the service access point SAPS for the synchronization are also shown, as well as the connection of framer F through physical layer interface <b>140</b> to internal interface <b>26</b>.

0063On the control link intermediate the processor P and the framer F is an in-band signaling encoder/decoder <b>138</b>. As explained hereinafter, the pre-start-up procedure is performed by a controller, which can take the form of the processor P or of a dedicated logic part (e.g., part of an ASIC) such as in-band signaling encoder/decoder <b>138</b>. The processor P is also shown as having access to a memory, such as NVRAM <b>142</b>. Moreover, line bit rate programming information is provided by processor P to framer F and physical layer interface, as depicted by line <b>144</b>.

0064The basic states of the pre-start-up procedure shown in <figref idref="DRAWINGS">FIG. 6</figref> include states <b>6</b>-A through <b>6</b>-E. Upon power on/reset of the base station portion, state <b>6</b>-A is entered. In state <b>6</b>-A, the controller creates a temporary available set (Temp_Set). As used herein, a “set” comprises one or more combinations of line bit rate and protocol. In state <b>6</b>-A the Temp_Set is set to either the stored last good known combination, or to a Configured_Set if no stored last good known combination exists. The Configured_Set is a pre-stored list of a complete set the equipment can handle or a pre-configured subset thereof.

0065At state <b>6</b>-B the controller initiates execution of the start-up procedure for the internal interface. If the internal interface <b>26</b> is a CPRI link, then the start-up procedure can be that illustrated in <figref idref="DRAWINGS">FIG. 11</figref>. If the start-up procedure as initiated at state <b>6</b>-B fails, the corresponding failing combination of protocol and or line bit rate is removed form the Temp_Set. If the Temp_Set is or becomes empty, the Temp_Set is set to the Configured_Set. Such can typically happen if a too optimistic Temp_Set is used, e.g. a wrongly stored last good known combination

0066Thus, as one of its aspects, the pre-start-up procedure involves storing one or more previously proven combinations of line bit rate and protocol as stored combination(s) for use on the internal interface. Prior to synchronization of the internal interface, the stored combination(s) are retrieved and included in the temporary available set (Temp_Set) of combinations of line bit rate and protocol (e.g., at state <b>6</b>-A). Thereafter the start-up procedure for the internal interface is initiated (state <b>6</b>-B) for the purpose of determining efficacy of the temporary available set.

0067In another of its aspects, after the pre-start-up procedure has initiated (at state <b>6</b>-B) the start-up procedure for the internal interface to determine efficacy of a set of combinations of line bit rate and protocol, the pre-start-up procedure removes a failed combination of line bit rate and protocol from the set should the start-up procedure fail.

0068Should the start-up procedure as initiated at state <b>6</b>-B result in synchronization of the physical layer (e.g., L<b>1</b> synchronization is established), the result of the start-up procedure at state <b>6</b>-B is a valid common combination (illustrated in <figref idref="DRAWINGS">FIG. 6</figref> as “Current_Item”). The resulting valid combination from the start-up procedure is stored by the controller and subsequently used for negotiating a best combination. As described hereinafter, the resulting valid combination from the start-up procedure is used if the start-up procedure using the best combination fails. The best combination is stored if the start-up procedure using it succeeds.

0069A successful synchronization at state <b>6</b>-B results in a transition to state <b>6</b>-C. In state <b>6</b>-C, the applications on both sides of the interface communicate and commonly agree (e.g., negotiate) on the best combination of line bit rate and protocol (which is labeled in <figref idref="DRAWINGS">FIG. 6</figref> as “Best_Item”). For example, this negotiation at state <b>6</b>-C can be performed by control software (SW) in radio equipment controller (REC) <b>22</b> talking with control software (SW) in radio equipment (RE) <b>24</b>.

0070If it is determined at state <b>6</b>-C that the Best_Item as negotiated is equal to the valid combination (“Current_Item”) which resulted from state <b>6</b>-B, at state <b>6</b>-<b>6</b> it is realized that the optimum combination of line bit rate and protocol has already been selected. Therefore, in this case, there is a direct transition to state <b>6</b>-E. If, on the other hand, the “Best_Item” as negotiated at state <b>6</b>-C is not equal to the valid combination which resulted from state <b>6</b>-B (i.e., the “Best Item” is not the “Current_Item”), then at state <b>6</b>-D the start-up procedure is entered with only the Best_Item as the available set.

0071Moreover, the temporary active set is configured to be the valid combination of line bit rate and protocol, and the valid combination of line bit rate and protocol is also included in a configured set of combinations of line bit rate and protocol.

0072If the start up procedure at state <b>6</b>-D is successful (which it should be) state <b>6</b>-E is entered. But if for any reason the start up procedure is unsuccessful, the state E is entered again, using the last good known combination (Current_Item) as “available set” to speed up the process of reaching state <b>6</b>-C again.

0073In transitions to state <b>6</b>-C, state <b>6</b>-D, and state <b>6</b>-E, the Temp_Set is set to the Current_Item, i.e. the Temp_Set in these cases equals a known good combination. In state <b>6</b>-C and <b>6</b>-E, the Temp_Set is also stored for fast acquisition in case of a reset.

0074From the foregoing it can be seen that, should synchronization of the physical layer by the start-up procedure succeed at state <b>6</b>-B , the pre-start-up procedure uses a valid combination of line bit rate and protocol in the available set for negotiating (at state <b>6</b>-C) between the radio equipment controller (REC) and the radio equipment (RE). A best combination of line bit rate and protocol is determined during the negotiating. Should the valid combination be agreed at state <b>6</b>-C to be the best combination during the negotiating, the start-up procedure is ended and state <b>6</b>-E is entered. On the other hand, should the valid combination not be the best combination, only the best combination of line bit rate and protocol is included in the available set, and thereafter the start-up procedure is restarted. At various junctures the temporary active set is set to be the valid combination of line bit rate and protocol in order to expedite processing should the start-up procedure fail.

0075The time to switch between different line bit rates within an “available set” is defined in the CPRI specification, and is very demanding. As another of its aspects, illustrated in part in <figref idref="DRAWINGS">FIG. 7</figref>, the pre-start-up procedure simplifies hardware and allows a longer time to switch between different line bit rates during state <b>6</b>-B.

0076In this optional aspect of <figref idref="DRAWINGS">FIG. 7</figref>, as step <b>6</b>-B′-<b>1</b> the pre-start-up procedure classifies the temporary available set into plural subsets, each subset of the temporary available set containing combinations of line bit rate and protocol having a same line bit rate. For example, the Temp_Set can be divided into k number of subsets, so that each Subset_k is defined as all items in Temp_Set which have a line bit rate equal to k. Then, as step <b>6</b>-B′-<b>2</b>, the pre-start-up procedure separately initiates the start-up procedure for the internal interface for each subset. In other words, for each k the start-up procedure is run with Subset_k. As previously, the transitions to and from state <b>6</b>-B are still valid.

0077The pre-start-up procedure can sequence in a predefined or preferred order the use of the subsets in the initiations of the start-up procedure. Since switching between different line bit rates takes time, this aspect of the pre-start-up procedure simplifies hardware design. By using this aspect, the pre-start-up procedure does not have repeatedly to perform a fast change between different line bit rates, but can instead use one bit rate, then let the “start-up” timer expire, and then test the next line bit rate. This allows a simple hardware implementation which is still compliant with the Common Public Radio Interface Specification Version 1.0 (Sep. 26, 2003) and Version 1.1 (May 10, 2004).

0078In another of its aspects illustrated in <figref idref="DRAWINGS">FIG. 9</figref>, the pre-start-up procedure classifies (as action <b>9</b>-<b>1</b>) the stored combinations into two classification. A first classification (<b>9</b>-<b>2</b>) is a best last time combination of line bit rate and protocol which was involved in a last successful execution of the start-up procedure. A second classification (<b>9</b>-<b>3</b>) is a union all combinations of line bit rate and protocol for which the synchronization of the physical layer has previously been successful during the start-up procedure. Capitalizing upon this classification, as action <b>9</b>-<b>4</b> the pre-start-up procedure can use the best last time combination as the temporary available set for initiating the start-up procedure for the internal interface. Then, if (as determined at action <b>9</b>-<b>5</b>) the start-up procedure fails with the best last time combination, the pre-start-up procedure can as action <b>9</b>-<b>6</b> resort to using the union of all combinations as the temporary available set for initiating the start-up procedure for the internal interface. If (as determined at action <b>9</b>-<b>7</b>) the start-up procedure fails with the union of all previously successful combinations, the pre-start-up procedure can as action <b>9</b>-<b>8</b> resort to the configured set. Both the best last time combination and the union of all previously successful combinations can be (separately) stored in non-volative RAM, such as NVRAM <b>142</b>.

0079The in-band signaling encoding/decoding (e.g., CPRI in-band signaling encoding/decoding) is either done by control software (SW) in the processor P or by a dedicated logic (e.g., part of an ASIC). The control of the line bit rate on the physical interface is either controlled directly by the control software (SW) in processor P or by the in-band signaling encoder/decoder <b>138</b>. The line bit rate choice is used in the framing (e.g., CPRI framing) and the physical layer interface.

0080Typically, the control software (SW) has the information about the Original Set, the Temp_Set, etc., and programs and the CPRI circuits (framer, physical layer, and encoder/decoder) when switching line bit rate. The protocol negotiation is typically done by the in-band signaling encoder/decoder <b>138</b> and also the C&amp;M link rate. The synchronization to a line bit rate is typically done by the framer F. As mentioned above, the negotiation of state <b>6</b>-C is done by the control software (SW) in the radio equipment (RE) <b>24</b> talking with the control software (SW) in the radio equipment controller (REC) <b>22</b>.

0081The Common Public Radio Interface Specification Version 1.0 (Sep. 26, 2003) and Version 1.1 (May 10, 2004) is very flexible concerning actual implementation of where the negotiations (protocol revision, C&amp;M rate) are to be performed. The time to answer is set so high that the software (SW) can read out the inband signaling, evaluate it, and write a new one (encoder/decoder in software). The negotiations are also made so simple that it can be implemented in hardware (e.g., in-band signaling encoder/decoder <b>138</b>). One implementation example is that the basic negotiation is performed by a hardware implementation of the “CPRI inband signaling encoder/decoder” and that the enhancements (outer loop, e.g., pre-start-up procedure) are done by the control software (SW). The one line bit rate at a time aspect described in <figref idref="DRAWINGS">FIG. 7</figref> will then move the line bit rate change from hardware to the control software (SW), making the hardware cheaper and simpler.

0082The invention has been described in a basic configuration in which one radio equipment controller (REC) <b>22</b> and one radio equipment (RE) <b>24</b> are connected by a single CPRI physical link. The invention is not limited to this configuration, but should be understood to be extended to other configurations including but not limited to those described in Common Public Radio Interface Specification Version 1.0 (Sep. 26, 2003) and Version 1.1 (May 10, 2004). For example, as illustrated in <figref idref="DRAWINGS">FIG. 10A</figref>, the invention may be implemented in a configuration in which several CPRI physical links can be used to enhance the system capacity required for large system configurations involving many antennas and carriers. Moreover, as illustrated in <figref idref="DRAWINGS">FIG. 10B</figref>, several radio equipment entities may be served by one radio equipment controller (REC) <b>22</b>.

0083The pre-start-up procedure as described above in one or more of its aspects has numerous advantages and facilitates numerous benefits. For example, the pre-start-up procedure combines automatic configuration (plug and play) with a fast restart, and in one example mode is fully compliant with Common Public Radio Interface Specification Version 1.0 (Sep. 26, 2003) and Version 1.1 (May 10, 2004). The pre-start-up procedure stores and retrieves one or more known good combination for faster start up. As an option, the pre-start-up procedure removes bad combinations of line bit rates and protocol when detected, and removes bad combinations of line bit rates when detected. In one of its aspects, the pre-start-up procedure tries the start up procedure first with a small set of combinations, and increasing the set when the first small set proves to be too small. Further, the pre-start-up procedure can add every successful combination to the known good set. In one of its aspects, the pre-start-up procedure runs the start up procedure one line bit rate at a time.

0084While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements.