Abstract:
A radio link transmission method that comprises transmitting data on a plurality of radio channels. The method allocates a portion of the capacity of each radio channel for transmission of identical data on the plurality of radio channels. The remaining capacity of each radio channel is allocated for transmission of unique data, which is different for each radio channel. The method further transmits the identical data on each radio channel of the plurality of radio channels, and transmits the unique data in the respective radio channels of the plurality of radio channels.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to communication systems, in particular to wireless systems adopting radio protection schemes. 
       BACKGROUND 
       [0002]    Wireless backhaul has recently been growing in popularity with both fixed and mobile carriers, which ask for support of different classes of services for both real-time applications, such as voice, and non real-time applications, such as web browsing and video streaming. The former services require high levels of availability, while lower levels are envisaged for the latter. 
         [0003]    In order to guarantee a certain degree of QoS and a certain level of service availability, wireless systems normally use some sort of radio protection scheme: the most commonly used radio protection is based on the principle of duplicating the radio link, and carrying the same traffic on both hops. 
         [0004]    The two most common configurations for radio protection are 1+1 hot standby and 1+1 working standby: 
         [0005]    Hot standby configuration is shown in  FIG. 1  and consists of two transmitters  3   a - 3   b  and two receivers  5   a - 5   b , tuned on the same frequency f 1 . Traffic  1  is split in two identical flows  1   a  and  1   b  and sent to two radio link indoor units  2   a  and  2   b , and from there to the two transmitters  3   a  and  3   b ; only transmitter  3   a  is active, while transmitter  3   b  is in standby. Transmitter  3   a  sends the same data to receivers  5   a  and  5   b , over the two channels  4   a  and  4   b . Data is collected by two further radio link indoor units  6   a  and  6   b , so that the resulting two traffic flows  7   a  and  7   h  are the same. The transmitter  3   b  transmits only if the transmitter  3   a  or the radio link indoor unit  2   a  experience problems. 
         [0006]    In working standby configuration there are still two transmitters and two receivers, but they are tuned on different frequencies; the traffic is duplicated and both transmitters are active in parallel, sending the same data.  FIG. 2  shows the most commonly implemented 1+1 working standby scenario: the traffic  1 , split in two identical flows  1   a  and  1   b , is sent to the transmitters  3   a  and  3   b  via the radio link indoor units  2   a  and  2   b . Both transmitters are active and tuned on a different frequency f 1  and f 2 . The traffic is then sent both by transmitter  3   a  to receiver  5   a  via channel  4   a , and by transmitter  3   b  to receiver  5   b  via channel  4   b . The received data is collected by the two radio link indoor units  6   a  and  6   b , so that the resulting two traffic flows  7   a  and  7   b  are the same. 
         [0007]    Most commonly, with respect to the need for protection, four different traffic typologies can be identified: circuit-switched traffic (typically voice), protected packet traffic, guaranteed packet traffic, which besides guarantees a maximum limit on delay, and best effort packet traffic, which carries non critical services such as web traffic or file transfers, and for which the network does not provide any guarantee that the data is delivered. 
         [0008]    In recent years the technology of Adaptive Modulation and Coding (AMC) has been developed with the aim of improving the channel bandwidth efficiency. 
         [0009]    The basic idea behind AMC is that the modulation and coding scheme on the communication channels is not fixed statically, but can vary dynamically over time in response to the varying quality of the radio link. 
         [0010]    The use of AMC in combination with protection allows for a more effective exploitation of the available bandwidth. At present two main schemes that build upon the 1+1 working standby configuration are known. 
         [0011]    The first solution consists in transmitting the same radio frames with the most spectral efficient modulation scheme on both links of the 1+1 configuration. This strategy maximizes the throughput in spite of protection, as the chosen best modulation might be not in accordance with channel condition of both links. 
         [0012]    The dual solution prefers the protection in spite of the throughput by transmitting the same radio frames with the lower modulation scheme between the two links. 
         [0013]    Known protection schemes do not consider any difference in the type of data traffic transported, that is, they protect all traffic, even the traffic that does not require protection such as guaranteed and best effort data, and this results in ineffective bandwidth utilization. 
       SUMMARY 
       [0014]    The aim of the present invention is to provide a new radio protection scheme that overcomes the above mentioned drawbacks, by guaranteeing high availability together with best efficiency in terms of available capacity in the radio channel. 
         [0015]    This aim and other objects which will become better apparent hereinafter are achieved by a radio link transmission method comprising transmitting data on a plurality of radio channels. The method allocates a portion of the capacity of each radio channel for transmission of identical data on the plurality of radio channels. The remaining capacity of each radio channel is allocated for transmission of unique data, which is different for each radio channel. The method further transmits the identical data on each radio channel of the plurality of radio channels, and transmits the unique data in the respective radio channels of the plurality of radio channels. 
         [0016]    The plurality of radio channels may be composed of two channels, which may optionally use different frequencies and/or use different polarizations. 
         [0017]    The plurality of radio channels may be in the microwave band and may optionally have different capacities. 
         [0018]    Furthermore, the plurality of radio channels may adopt different modulation schemes, and each radio channel may adopt a modulation scheme which changes over time. 
         [0019]    The portion of each radio channel capacity allocated for transmission of identical data may be constant over time. 
         [0020]    According to another aspect of the invention, a radio link transmission apparatus for transmitting data on a plurality of radio channels is provided. The apparatus comprises means for allocating a portion of the capacity of each radio channel of the plurality of channels for identical data and for allocating the remaining portion of the capacity for unique data. 
         [0021]    The apparatus further comprises means for transmitting the identical data on each radio channel of the plurality of radio channels, and means for transmitting the unique data on each radio channel of the plurality of channels; the unique data are different for each radio channel of the plurality of radio channels. 
         [0022]    The plurality of radio channels may be composed of two channels and may use different frequencies and/or different polarizations. 
         [0023]    The radio channels may be in the microwave band and may have different capacities. 
         [0024]    The means for transmitting the identical data and the means for transmitting the unique data may comprise respective modulators configured to adopt modulation schemes different from one modulator to another. 
         [0025]    The modulation scheme for each radio channel may be adaptive. 
         [0026]    Optionally, the portion of each radio channel capacity allocated for transmission of identical data may be constant over time. 
         [0027]    The means for transmitting identical data may comprise a splitter, having an input for receiving the identical data and a plurality of outputs for transmitting the identical data on all of the plurality of channels. 
         [0028]    The means for allocating may comprise at least one multiplexer for each channel of the plurality of channels, which is configured to aggregate the identical data with the unique data of each channel. 
         [0029]    The aim and the objects of the invention are also achieved by a radio link comprising the above radio link transmitting apparatus and a radio link receiving apparatus. 
         [0030]    The radio link receiving apparatus may comprise means for separating the identical data from the unique data in each channel. 
         [0031]    It is noted that the proposed configuration can be used for carrying both protected and unprotected traffics on the same radio link, in which only the traffic that need protection is duplicated, thus allowing to increase the total traffic capacity. 
         [0032]    Moreover, adopting Adaptive Modulation and Coding allows to apply the most suitable AMC scheme independently on each link of the working standby configuration. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0033]    Further characteristics and advantages of the invention will become better apparent from the detailed description of particular but not exclusive embodiments, illustrated by way of non-limiting examples in the accompanying drawings, wherein: 
           [0034]      FIG. 1  shows a known 1+1 hot standby protection scheme. 
           [0035]      FIG. 2  shows a known 1+1 working standby protection scheme. 
           [0036]      FIG. 3  represents the combination of different traffic typologies both in fixed and adaptive modulation scheme according to the present invention. 
           [0037]      FIG. 4  shows a preferred embodiment of the transmitting system for combining protected and unprotected traffic according to the present invention. 
           [0038]      FIG. 5  shows a preferred embodiment of the receiving systems for recovering protected and unprotected traffic according to the present invention. 
           [0039]      FIG. 6  shows the maximum available traffic capacity of the two radio links of the embodiment for each handled typology of traffic with reference to a practical example. 
           [0040]      FIG. 7  shows a protection scheme according to the invention, when link conditions are favorable. 
           [0041]      FIG. 8  shows a protection scheme according to the invention, when link conditions worsen. 
       
    
    
     DETAILED DESCRIPTION 
       [0042]      FIG. 3  shows the combination of different traffic typologies on the two channels of a working standby configuration according to the invention, both in a fixed modulation scheme and in an adaptive modulation scheme. 
         [0043]    If the channels are in fixed scheme mode, the capacity, depicted by line  30 , is constant, and the system carries three typologies of traffic: protected circuit-switched data, protected packet data and guaranteed packet data. The traffic is split in two payloads  10   a  and  10   b , which respectively travel at the frequencies f 1  and f 2  of the 1+1 working standby configuration. Protected circuit-switched data  11  and protected packet data  12  are duplicated in the two payloads and then protected. On the contrary, different guaranteed packet data  13  and  14  are respectively carried by the two payloads  10   a  and  10   b , and then they are unprotected and guaranteed with an availability level dependent on the quality level of the modulation scheme. 
         [0044]    When adaptive modulation is utilized, the total capacity varies over time. In this case, an additional typology of traffic, best effort traffic, may be present in addition to the other typologies of traffic described above. As in the fixed modulation case, two payloads  20   a  and  20   b  flow at the respective frequencies f 1  and f 2  of the 1+1 working standby configuration. 
         [0045]    Protected circuit-switched data  21  and protected packet data  22  are duplicated in the respective payloads  20   a  and  20   b , while different unprotected data is sent in payloads  20   a  and  20   b . In particular, payload  20   a  carries guaranteed packet data  23  and best effort packet data  24  which are different from the guaranteed packet data  25  and the best effort packet data  26  which are carried by the other payload  20   b.    
         [0046]    The total capacity allocated to protected traffic  21  and  22  is less or equal to the minimum modulation scheme capacity, indicated by line  30  in  FIG. 3 . The capacity allocated for guaranteed packed data  23  and  25  (if any) is determined by the difference between the minimum modulation capacity and the capacity configured for protected data. The available capacity for best effort data  24  and  26  is varying and depends on the actual modulation scheme: lines  40  and  50  in  FIG. 3  depict the current maximum modulation scheme on the first and the second channel f 1  and f 2 . Best effort data is not only not duplicated and then not protected, but the quantity of data carried can vary in the two payloads reflecting the different conditions of the two radio channels. 
         [0047]    A possible embodiment of the system needed to perform the aggregation and separation of the two traffic payloads is now discussed with reference to  FIG. 4 . 
         [0048]    At the transmitter  100  of the radio link, a first multiplexer  110  is provided for aggregating the circuit-switched data and/or the protected packet data  101 , which may be of the same or different rates, synchronous, plesiochronous or asynchronous, obtaining the protected composite data stream  102 . 
         [0049]    In order to simplify recovery of the individual data streams at the receiver side  200 , a generator of synchronization information  120  may be further added to the composite data stream via the aggregator  130 . 
         [0050]    The output of the first multiplexer or, as shown in  FIG. 4 , of the aggregator  130  is fed to two second multiplexers  141  and  142 , so as to duplicate the protected composite data stream and to obtain two streams of identical data. The second multiplexers  141  and  142  also comprise at their inputs different unprotected traffic streams  103  and  104 , respectively, which also may be of the same or different rates, synchronous, plesiochronous or asynchronous and which will be herein referred to also as unique data streams. 
         [0051]    Each of the duplicated protected composite data streams  105  and  106  is then aggregated with different unique data streams  103  and  104 , respectively. 
         [0052]    Furthermore, respective generators of path specific control signaling  151  and  152  are provided in input to third multiplexers  161  and  162 , which also receive the multiplexed traffic from the second multiplexers  141  and  142 , respectively. 
         [0053]    The outputs of the third multiplexers  161  and  162  which carry the resulting assembled composite data streams are fed to modulation devices  171  and  172 , respectively, and finally to radio transmitters, not shown. 
         [0054]    At the receiver  200  of the radio link, as shown in  FIG. 5 , demodulation devices  211  and  212  may be provided for each channel f 1  and f 2  to recover the composite data streams from the radio signals. Synchronization means  221  and  222  may be provided downstream of the demodulation devices  211  and  212  for carrying out extraction of synchronization information and alignment of the individual demodulated composite data streams  213  and  214 , using the synchronization information added by the generator  120  in the transmitter  100 . 
         [0055]    A selector  240  is connected downstream of the synchronization means  221  and  222  for selecting the best protected traffic by using the quality of the transmission paths. 
         [0056]    A first demultiplexer  260  is connected to the output of the selector  240  for extracting the protected data and obtaining the protected data traffics  201 . 
         [0057]    Analogously, path specific control signaling extraction devices  231  and  232  are provided for allowing composite data decoding. Second demultiplexers  251  and  252  are instead connected to the output of the path specific control signaling extraction devices  231  and  232  in order to extract unprotected data and obtain the unprotected data traffics  203  and  204 . When synchronization or alignment is lost, only the unprotected data are extracted. 
         [0058]    An embodiment of the invention in which adaptive modulation is adopted will be detailed through a practical example in which the radio link implementing the invention is configured as follows. The modulation schemes adopted in adaptive modulation are 4 QAM, 16 QAM, 64 QAM, and 128 QAM, the protected circuit-switched traffic capacity is 16 Mbps and the protected packet traffic capacity is 12 Mbps. 
         [0059]    Considering that a plausible capacity of the most robust modulation scheme (4 QAM) can be 48 Mbps, the guaranteed packet traffic capacity results 48-16-12=20 Mbps. 
         [0060]    In  FIG. 6 , the maximum available traffic capacity of the two radio links of the embodiment are shown, for each handled typology of traffic. 
         [0061]    During period with favorable propagation conditions, shown in  FIG. 7 , the two radio links work at the highest modulation scheme, that is 128 QAM. According to the table of  FIG. 6 , the traffic capacities would be of 16 MBps for circuit switched data  21 , 12 Mbps for protected packet data  22 , 20 Mbps for guaranteed packet data  23  and  25 , and 112 Mbps for best effort packet data  24  and  26 . 
         [0062]    Assuming that slight fading conditions affect the first radio link  4   a , the modulation is adaptively changed to more robust scheme, 64 QAM. The traffic capacities will now remain unchanged for protected and guaranteed data, while best effort data in the first hop would decrement to 92 Mbps. 
         [0063]    When propagation conditions worsen and affect both radio links  4   a  and  4   b , as shown in  FIG. 8 , their modulations are adaptively changed to more robust schemes, e.g. 16 QAM and 64 QAM, respectively. The traffic capacities will vary accordingly, diminishing the capacity for best effort data  24  and  26  on both hops respectively to 48 and 92 Mbps. 
         [0064]    It has been shown that the invention fully achieves the intended aim and objects, since it allows to combine radio protection with efficient bandwidth utilization. 
         [0065]    The invention advantageously supports different quality of service classes, and introduces no changes on protection of protected traffic, but doubles available capacity for unprotected traffic, so that unprotected data throughput is approximately doubled with respect to working standby protection offered by present state of the art. 
         [0066]    Furthermore the invention allows to fully exploit the gain in bandwidth utilization obtained by the use of an Adaptive Modulation and Coding scheme, by suggesting that adaptive modulation functionality is independently applied on the two radio links of the working configuration. In this way, the optimal modulation is always selected on each radio link and the spectral efficiency of the single radio link resource is improved. 
         [0067]    Besides the invention provides a simple and easy to implement solution, that does not require additional frequencies or supplementary equipment. 
         [0068]    The invention also provides a hitless protection of circuit-switched data, and supports prioritization of packet data traffic, transport of guaranteed packet data and hitless protection of packet data. 
         [0069]    Clearly, several modifications will be apparent to and can be readily made by the skilled in the art without departing from the scope of the present invention. 
         [0070]    For example it is straightforward for the skilled in the art extending the described scheme to a scenario comprising more than two channels, or considering a system in which the differentiation of the two channels is performed on polarization instead of frequency. 
         [0071]    Therefore, the scope of the claims shall not be limited by the illustrations or the preferred embodiments given in the description in the form of examples, but rather the claims shall encompass all of the features of patentable novelty that reside in the present invention, including all the features that would be treated as equivalents by the skilled in the art. 
         [0072]    Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly, such reference signs do not have any limiting effect on the interpretation of each element identified by way of example by such reference signs.