WORKING STANDBY PROTECTED RADIO LINK

Technical Field

The present invention relates to communication systems, in particular to wireless systems adopting radio protection schemes.

Background

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.

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. One of the most common configurations for radio protection is 1+1 working standby.

A working standby configuration consists of two transmitters and two receivers, tuned on different frequencies. Traffic is duplicated and sent to the two transmitters, which are active in parallel and therefore transmit the same data over two hops. Figure 1 shows the most commonly implemented 1+1 working standby scenario: the traffic 1 is split in two identical flows la and lb which are each sent to a respective transmitter 3 a and 3b via a corresponding radio link indoor unit 2a and 2b. Both transmitters 3 a and 3b are active and tuned on a different frequency fl and f2. The traffic is therefore sent both by transmitter 3 a to receiver 5 a via channel 4a, and by transmitter 3b to receiver 5b via channel 4b. The received data is collected by two radio link indoor units 6a and 6b, so that the resulting two traffic flows 7a and 7b are the same.

In recent years the technology of Adaptive Modulation and Coding (AMC) has been developed with the aim of improving the channel bandwidth efficiency. 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. The use of AMC in combination with protection allows for a more effective exploitation of the available bandwidth.

The majority of 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.

WO 2010/022792 describes the implementation of a system which makes more efficient use of two or more radio channels in a working standby protected hop when used for packet link transport. The method described therein 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. The plurality of radio channels may adopt different modulation schemes, and each radio channel may adopt a modulation scheme which changes over time.

When the above feature described in WO 2010/022792 is disabled, packet link data is duplicated and transmitted over both hops in a protected pair, in the same way as the most commonly known implementations of working standby protected configurations. In this case, both links have the same payload, which means that they carry the same amount of actual data. When instead the above feature described in WO 2010/022792 is enabled, the packed traffic, or at least the less critical part thereof, is sent unprotected on both working hops, bonding together the two single packet links of the two hops. In this way the total packet link capacity is greatly increased, when compared to standard working standby links. In this way, packet link capacity for the protected pair in working standby configurations is significantly increased, while retaining at the same time the protection mechanism for critical data.

The method envisaged in WO 2010/022792, implemented in combination with AMC, has shown some limitations when the two links in the working standby protected hop request different modulation orders, due to differing quality of the radio links of the two channels.

One solution to these requests of different modulation orders is that of choosing the extended capacity mode, where preference is given to the amount of data transmitted on the protected pair in working standby configuration. This is achieved by setting the lowest requested modulation order for both links and send data traffic on both links. The traffic is therefore sent over two frames, one for each link. More specifically, for each data request two bytes are read: the first byte is put on the the first transmission link and the second byte is put on the second transmission link of the working standby protected hop.

Another solution is that of choosing the protection mode, that is, protecting the packet traffic in the standard working standby configuration. This is achieved by choosing the highest PHY for the link and therefore switching the system to a normal working standby configuration. In this case, each data byte is read and put on both links, but due to its worse quality one of the two radio links is not active.

Either of the above solution lead to a waste of capacity available on the radio link channels. In the first case, capacity is lost by forcing the radio link channel which experience better quality to lower its modulation order to the maximum allowable on the other radio link channel which experience worse quality. The link which could be set to the higher modulation order is instead forced to downshift and there fore looses the related traffic capacity. In the second case, the link with the lower modulation order is set as unused due to bad quality of the radio link, and therefore the related traffic capacity is entirely lost.

Summary

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 link channel.

The aim and other object which will become better apparent hereinafter are achieved by a radio link transmission method comprising transmitting data on a plurality of n radio channels. The method allocates at least a portion of capacity of each radio channel for transmission of unique data, which is different for each radio channel. The method segments an input data stream into n pieces of segmented data having each its own determined length, and transmits said n pieces of segmented data stream as unique data in the respective radio channels. The length of each of the n pieces of segmented data is such that its transmission in the respective radio channel is lasting an equal amount of time for all n pieces of segmented data.

The length of the n pieces of segmented data can be calculated so as to satisfy the equation:

FLi / Cl = FL ₂ / C2 = ... = FL _n / 0? (1) where FLi, FL ₂ ,...,FL _n is the length of the n pieces of segmented data stream, and CI, C2, Cn is the allocated portion of capacity of each radio channel.

Each piece of segmented data stream can be preceded by a start signal sent on each radio channel, in order to get the receiver aligned and readi to receive and reassembling segmented data.

The plurality of radio channels can use different frequencies.

Furthermore, said plurality of radio channels can be composed of two channels. In this last case, the ratio between the lengths of both frames running on different modulation orders has to equal the ratio between the capacities of the two links. In this way both frames are aligned in time even if they have different length.

According to another aspect of the invention, a radio link transmitting apparatus for transmitting data on a plurality of radio channels is provided. The apparatus comprises means for allocating at least a portion of capacity of each radio channel for transmission of unique data. This unique data is different for each radio channel. The apparatus further comprises means for segmenting an input data stream into n pieces of segmented data having each its own determined length. The apparatus comprises also means for transmitting said n pieces of segmented data stream as unique data in the respective radio channels. Means are also provided for calculating the length of each of the n pieces of segmented data so that its transmission in the respective radio channel is lasting an equal amount of time for all n pieces of segmented data.

The means for calculating the length of the n pieces of segmented data are adapted to perform a calculation so as to satisfy the equation

FLi / C l = FL ₂ / C2 = . .. = FL _n / 0? (2) where FLi, FL ₂ ,. .. ,FL _n is the length of the n pieces of segmented data stream, and CI , C2, Cn is the allocated portion of capacity of each radio channel.

As mentioned above, each piece of segmented data stream can be preceded by a start signal sent on each radio channel, said plurality of radio channels can use different frequencies, and said plurality of radio channels can be composed of two channels. 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.

A general concept of the present invention is that of keeping the plurality of radio link channels active at their modulation order even if they differ. The present invention addresses the limitations of the current implementations, where data traffic is sent over both radio link channels on frames that have a fixed length, and which needs to be aligned in time on both links so as to prevent byte misordering at the receiver side. More specifically, the present invention removes the constraint of fixed frame length, in term of byte size, for all radio link channels, and the constraint of same modulation order for all radio link channels, so as to get full capacity for the packet data traffic. The invention provides the single constraint of fixed frame length in terms of time duration for all radio link channels.

The present invention provides for frame sizes which in term of number of bytes are not fixed and equal for all radio link channels. Their sizes depends instead on the capacity available at any given moment for the given modulation order. This gives a degree of freedom which allows to use different modulation orders for each radio link channel, still keeping the frames synchronized in time.

Brief description of the drawings

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:

Figure 1 shows a known 1+1 working standby protection system used as a base transmission system for the present invention.

Figure 2 represents the transmission of data over the working standby protection system of Figure 1 when modulation orders are the same for both radio links channels.

Figure 3 represents the transmission of data over the working standby protection system of Figure 1 when modulation orders are different for the two radio links channels.

Figure 4 shows a transmitting system for protected and unprotected traffic which can be used in connection with a working standby protection system. Detailed description

Figure 2 represents the transmission of data over the working standby protection system of Figure 1 , when modulation orders are the same for both radio link channels. The drawing is merely exemplary and it is provided as an aid to explain concepts underlying the present invention. More in detail, it is assumed that a input flow of data 10 has to be transmitted over a radio link configured as a 1+1 working standby protection system as represented in Figure 1. Although the present example refers to a system involving only two radio link channels 4a and 4b, it will be clear from what follows that the invention can be readily applied also to a system involving more than two radio link channels configured as a working standby protection system.

Input data flow 10 comprises a number of info-blocks which are atomic pieces of data of the total input data stream. Info-blocks can generally be defined as bits or bytes or multiples thereof, and in the example of Figure 2 they are assumed as being individual bytes. When the radio channels 4a and 4b have the same modulation order and therefore the same capacity CI = C2, the input data flow 10 is divided in equal frames or sub-pieces 11a and l ib of same size P bytes, which are sent each to a corresponding radio channel 4a and 4b. This corresponds to the usual behavior of a working standby protection system where in particular odd data bytes are put on sub-piece 11a and even data bytes are put on sub-piece l ib. At the receiving end of the radio channels 4a and 4b, the sub-pieces 11a and 1 lb are received and then reassembled into a unique consistent output data flow 12.

When one of the two radio channels need to change the modulation order because its quality has changed, for example has worsened, then the system can keep both links active if the frames, i.e. sub-pieces, of both radio channels satisfy the following formula:

FLi / Cl = FL ₂ / C2 (2) where FL _a , Fib are the frame (or sub-piece) length in bytes (or info-blocks) respectively on radio channels 4a, 4b, and CI, C2 are the capacities of the same radio channels.

In more general terms, if there are n radio channels, the formula can be generalized as:

FLi / Cl = FL ₂ / C2 = ... = FL _n / 0? (1) Figure 3 represents the transmission of data over the working standby protection system of Figure 1 when modulation orders are different for the two radio channels. Even in this case the drawing is merely exemplary and is provided as a mere aid to explain concepts underlying the present invention. Moreover, the example does not constitute a limitation of the invention to a 1+1 working standby protection system, but it can be readily understood as applicable also to a system involving more than two radio channels.

The input data stream 10 is divided into pieces 13 whose dimension is M+N info-blocks, where M and N are integers which, multiplied by a common factor X, give the capacity CI, C2 of radio channels 4a, 4b, respectively. In other words, the common factor X is the greatest common divisor of capacities CI, C2., so that CI = M x X and C2 = N x X.

A segmenting section, known per se, splits pieces 13 of input data stream 10 into two frames or sub-pieces 14a, 14b having a length of M info- blocks and N info-blocks, respectively. These sub-pieces 14a, 14b are each sent to a radio channel 4a, 4b as substreams SI, S2, preferably preceded by a start signal which is sent over the two radio channels in order to get the receiver aligned and ready to receive the segmented data. Because of the different capacity of each radio channel 4a and 4b, each frame or sub-piece 14a, 14b has the same duration in time t _f . At the receiver side the data will therefore be automatically aligned in time because M info-blocks on radio channel 4a have the same duration of N info-blocks on radio channel 4b. A reassembling section, known per se, will then merge both substreams SI and S2 according to the segmentation algorithm, that is, reassembling the two frames or sub-pieces 14a and 14b into a single piece 15 of the output data stream 12.

As a simple example, it can be assumed that capacity of radio channels 4a, 4b is

CI = 180 Mbit/s = 12 x 15 Mbit/s

C2 = 204 Mbit/s = 12 x 17 Mbit/s

where, adopting the convention used in the description of Figure 3, common factor X = 12, M = 15 and N = 17.

If we define the info-block as a byte, the total input data stream 10 is divided into pieces of 17+15 = 32 bytes each. The segmenting section will split these 32-byte pieces into two sub-pieces 14a, 14b whose length is 17 bytes and 15 bytes, respectively. A "start of substreams" signal is then put as a header of each substream SI, S2 to make the receiver aligned. Substream SI is sent through the radio channel 4a and substream S2 is sent through the radio channel 4b. Both substreams SI and S2 have the same duration t _f on the link although they carry a different number of bytes. For this reason the substreams will be aligned at the receiver side where they can be reassembled into a single piece 15 of the output data stream 12, contaning 17+15 = 32 bytes which are correctly ordered so as to equal the original piece of input data stream 13.

A further example is made here considering a working standby protection scheme having a channel space of 28 MHz, and where the conditions of the radio link have determined the request for a modulation order 512 QAM on radio channel 4a and modulation order 256 QAM of radio channel 4b. The respective capacities are therefore 203 Mbit/s on radio channel 4a and 181 Mbit/s on radio channel 4b.

The application of formula (1) above can lead to a solution where the frame or sub-piece 14a sent as a substream SI on radio channel 4a has a length of 262144 bytes, while the frame or sub-piece 14b sent as substream S2 on radio channel 4b has a length of 233734 bytes. Such a solution which is rendered possible by the present invention renders it possible to exploit the full capacity of the system, that is, 203 + 181 = 384 Mbit/s. On comparison, if the lowest modulation order had been adopted on both radio links the total capacity would have been 181 + 181 = 362 Mbit/s, with a loss of 12 Mbit/s of capacity with respect to the capacity achieved by the present invention. If instead one had retained the highest modulation order on one radio channel only, then the capacity would have been 203 Mbit/s, with a net loss of 181 Mbit/s with respect to the total capacity achieved by the present invention.

In Figure 4 an example transmitter apparatus is illustrated. 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. A generator of synchronization information 120 may be further added to the composite data stream. A segmentator 130 divides the input data stream into two pieces of segmented data 105, 106 having each its own determined length. A calculator 181 calculates the length of the two pieces of segmented data so that its transmission in the respective radio channel is lasting an equal amount of time for the two pieces of segmented data.

The output of the segmentator 130 is fed to two second multiplexers 141 and 142 which may also comprise at their inputs different unprotected traffic streams 103 and 104, respectively, which also may be of the same or different rates. Respective generators of path specific controlling 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. 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 3 a, 3b of Figure 1.

At the receiver of the radio link, demodulation is effected in a similar, although specular, way as the transmitter.

From the above detailed description it is clear that the capacity achievable from the present invention on a working standby protection scheme will always be maximized, so that all the available data capacity is used for data transport. As a consequence, the spectrum efficiency is optimized and the Ethernet capacity is always at its maximum availability. Moreover, the Ethernet link becomes a real Ethernet 2+0 featuring Adaptive Modulation in every and each real condition, be it weather caused fading, interference caused fading, etc.

Naturally, the principle of the invention remaining the same, the embodiments and specific details can be varied and modified without departing from the scope of the invention as defined in the appended claims.