System and method for transmission symbol arrangement for reducing mutual interference

A method for operating a first device includes determining a spreading pattern associated with the first device, placing a pilot signal associated with the first device into resources of a first transmission symbol in accordance with the spreading pattern, and transmitting the first transmission symbol to a second device.

TECHNICAL FIELD

The present disclosure relates generally to digital communications, and more particularly to a system and method for transmission symbol arrangement for reducing mutual interference.

BACKGROUND

In general, a pilot signal or a reference signal is transmitted by a transmitting device, such as an evolved NodeB (eNB) and/or a user equipment (UE), to help a receiving device in decoding the transmission by assisting in channel estimation. However, if two or more transmitting devices simultaneously transmit their pilot signals on the same network resources, mutual interference occurs and channel estimation performance decreases. Hence, overall communications system performance degrades.

SUMMARY OF THE DISCLOSURE

Example embodiments of the present disclosure which provide a system and method for transmission symbol arrangement for reducing mutual interference.

In accordance with an example embodiment of the present disclosure, a method for operating a transmitting device is provided. The method includes determining, by the transmitting device, a spreading pattern associated with the transmitting device, and placing, by the transmitting device, a pilot signal associated with the transmitting device into resources of a first transmission symbol in accordance with the spreading pattern. The method also includes transmitting, by the transmitting device, the first transmission symbol to a receiving device.

In accordance with another example embodiment of the present disclosure, a method for operating a receiving device is provided. The method includes determining, by the receiving device, a spreading pattern associated with a transmitting device, and receiving, by the receiving device, a first transmission symbol from the transmitting device. The method also includes detecting, by the receiving device, a pilot signal associated with the transmitting device in resources of the first transmission symbol in accordance with the spreading pattern.

In accordance with another example embodiment of the present disclosure, a transmitting device is provided. The transmitting device includes a processor, and a transmitter operatively coupled to the processor. The processor determines a spreading pattern associated with the transmitting device, and places a pilot signal associated with the transmitting device into resources of a first transmission symbol in accordance with the spreading pattern. The transmitter transmits the first transmission symbol to a receiving device.

In accordance with another example embodiment of the present disclosure, a receiving device is provided. The receiving device includes a processor, and a receiver operatively coupled to the processor. The processor determines a spreading pattern associated with a transmitting device, and detects a pilot signal associated with the transmitting device in resources of a first transmission symbol in accordance with the spreading pattern. The receiver receives the first transmission symbol from the transmitting device.

One advantage of an embodiment is that more simultaneous UE transmissions are supported without suffering decreased channel estimation performance.

A further advantage of an embodiment is that with the increased number of simultaneous UE transmissions, UEs can transmit more frequently in general.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The operating of the current example embodiments and the structure thereof are discussed in detail below. It should be appreciated, however, that the present disclosure provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed are merely illustrative of specific structures of the disclosure and ways to operate the disclosure, and do not limit the scope of the disclosure.

One embodiment of the disclosure relates to transmission symbol arrangement for reducing mutual interference. For example, a transmitting device determines a spreading pattern associated with the transmitting device, places a pilot signal associated with the transmitting device into resources of a first transmission symbol in accordance with the spreading pattern, and transmits the first transmission symbol to a receiving device.

The present disclosure will be described with respect to example embodiments in a specific context, namely sparse code multiple access (SCMA) and/or low density signature (LDS) communications systems that use pilot signals to help improve channel estimation performance. The disclosure may be applied to standards compliant communications systems, and non-standards compliant communications systems, that use SCMA and/or LDS.

FIG. 1illustrates an example communications system100. Communications system100includes an eNB105serving a plurality of UEs, such as UE110, UE112, and UE114. In general, communications to and from a UE pass through eNB105. However, in a machine-to-machine (M2M) mode, UEs may be able to communicate directly without going through eNB105. Communications system100may also include a relay node (RN)115. RN115may use network resources of eNB105to help improve coverage and overall performance. As shown inFIG. 1, RN115may serve UE114to help improve coverage for UE114. Furthermore, eNB105and RN115may simultaneously transmit to UE114to further improve overall performance.

It is noted that an eNB may also be commonly referred to as a base station, NodeB, controller, communications controller, and the like. Similarly, a UE may also be commonly referred to as a mobile station, mobile, user, subscriber, terminal, and the like.

While it is understood that communications systems may employ multiple eNBs capable of communicating with a number of RNs and UEs, only one eNB, and a number of RNs and UEs are illustrated for simplicity.

FIG. 2illustrates a diagram of example orthogonal frequency division multiplexed (OFDM) symbols200in a Third Generation Partnership Project (3GPP) Long Term Evolution (LTE) compliant communications system. An OFDM symbol is an example of a transmission symbol. In general, OFDM symbols, such as OFDM symbols200includes a plurality of network resources and may include time resources, frequency resource, or a combination of time and frequency resources (individual blocks inFIG. 2represent a time-frequency resource of orthogonal frequency division multiple access (OFDMA), also commonly referred to as a tone). Time resources may be referred to as time slots and frequency resources may be referred to as tones. As an example, OFDM symbols200include a time slot205and a time slot210and tone215and tone220. An individual network resource may be referred to by a combination of its time resource and frequency resource. As an example, network resource225may be referred to as tone215of time slot205.

Network resources of OFDM symbols200may contain data (shown as network resources labeled “D”), pilot signals (shown as network resources labeled “P”), control signals, or a combination thereof. In a 3GPP LTE compliant communications system, pilot signals are transmitted in specified time slots, such as time slot210, to help a receiving device perform channel estimation. Multiple transmitting devices may transmit their pilot signals in the same time slot. Accurate channel estimation may be necessary to have good data detection performance.

Code division multiplexing (CDM) is used in the transmission of pilot signals to support the transmission of pilot signals by the plurality of transmitting devices. CDM is sufficient to achieve good channel estimation performance when the number of transmitting devices is low. However, when the number of transmitting is large, mutual interference may become a significant problem and poor channel estimation performance results. Therefore, there is a need for a system and method for transmission symbol arrangement for reducing mutual interference.

In a sparse code multiple access (SCMA) or a low density signature (LDS) communications system, data is spread in accordance with a SCMA codeword, or a LDS spreading signature , respectively. Each SCMA codeword or LDS spreading signature comprises a sequence of values, generally presented as zero and non-zero values. Collectively, the zero and non-zero pattern of SCMA codewords and/or LDS spreading signatures may be referred to as spreading patterns. SCMA and LDS are used for multiplexing different layers of data. LDS uses repetitions of the same symbol on layer-specific nonzero position in time or frequency. As an example, in LDS-OFDM a constellation point is repeated (with some possible phase rotations) over nonzero frequency tones of a LDS block. SCMA is a generalization of LDS where a multidimensional codebook is used to spread data over tones without necessarily repeating symbols.

SCMA is a modulation technique that encodes data streams, such as binary data streams into multidimensional codewords selected from SCMA codebooks. SCMA directly encodes the data stream into multidimensional codewords and circumvents quadrature amplitude modulation (QAM) bits to symbol mapping, which may lead to coding gain over conventional QAM modulation and LDS spreading. Notably, SCMA encoding techniques convey data streams using a multidimensional codeword rather than a QAM symbol.

Additionally, SCMA encoding provides multiple access through the use of different codebooks for different multiplexed layers, as opposed to the use of different spreading sequences (or signatures) for difference multiplexed layers, e.g., a LDS signatures in LDS, as is common in conventional CDMA encoding. Furthermore, SCMA encoding typically uses codebooks with sparse codewords that enable receivers to use low complexity algorithms, such as message passing algorithms (MPA), to detect respective codewords from combined codewords received by the receiver, thereby reducing processing complexity in the receivers.

FIG. 3aillustrates example OFDM symbols300with pilot signals fully occupying a single time slot. OFDM symbols300may be an example of OFDM symbols transmitted in a SCMA or LDS communications system. Pilot signals transmitted by transmitting devices fully occupy a time slot305, while data transmitted by the transmitting devices are spread in accordance with a spreading pattern, such as a low density signature in a LDS communications system or a sparse codeword in a SCMA communications system.FIG. 3aillustrates data transmitted by a transmitting device with spreading pattern 0 0 1 1. It is noted that data transmitted by other transmitting devices are not shown inFIG. 3ato maintain clarity.

FIG. 3billustrates example time slots350containing pilot signals transmitted by a plurality of transmitting devices. It is noted that the pilot signals may be transmitted by the transmitting device that are representative of Third Generation Partnership Project (3GPP) Long Term Evolution (LTE) compliant transmitting devices. Since the pilot signals transmitted by the plurality of transmitting devices fully occupy the tones, there is significant mutual interference. As shown inFIG. 3b, the pilot signals transmitted by UEs2-6(UE2, UE3, UE4, UE5, and UE6) induce interference to UE1.

Since the pilot signals transmitted by each of the plurality of transmitting devices collide with every other transmitting device and suffer heavy mutual interference, a large number of active transmitting devices typically cannot be supported. Furthermore, transmission power is supported on tones which are not needed to estimate the channels corresponding to the tones. As an illustrative example, referring back toFIG. 3a, to help ensure good performance, only the channels corresponding to tones labeled “D” need to be estimated. However, in LTE, the pilot signals are transmitted in all of the tones.

According to an example embodiment, it may be possible to exploit sparsity in the frequency domain present in a SCMA or LDS communications system. The data transmitted of a transmitting device may be spread using a spreading pattern associated with the transmitting device.

FIG. 4illustrates a diagram of sequences400highlighting an example data arrangement technique. Sequences400include a first data stream405illustrates data after being spread by spreading pattern 0 0 1 1. It is noted that the use of different spreading patterns will result in different sequences. A second data stream410illustrates the data after arrangement with the data arrangement technique.

According to an example embodiment, the data arrangement corresponds to the spreading pattern associated with the transmitting device. As an illustrative example, consider the following scenario: a time slot with a total of 16 tones, and a spreading pattern of 0 0 1 1. Therefore, the total number of tones is divided into L sub-blocks, where L is the length of the spreading pattern (e.g., SCMA codeword or LDS spreading signature), inFIG. 4, L=4. Let the data stream contain C spreading patterns (e.g., SCMA codewords or LDS spreading signatures), inFIG. 4, C=4. The total length of the data stream is C×L tones. As shown inFIG. 4, C×L=16 tones. The number of sub-blocks in the data after arrangement is L, where each sub-block contains C tones. Hence, there are L=4 sub-blocks with C=4 tones in each sub-block. The example data arrangement technique may be expressed as:

The I-th element of the k-th spreading pattern, e.g., SCMA codeword or LDS sequence, of a first data stream is placed in the k-th tone of the I-th sub-block of a second data stream, where the second data stream is the first data stream after application of the data arrangement.

As an illustrative example, consider tone412that is the first element of the first spreading pattern (e.g., SCMA codeword or LDS sequence). Tone412is placed in the first tone of the first sub-block (shown as tone414) in accordance with the example data arrangement technique. Similarly, tone416is the second element of the first spreading pattern. Tone416is placed in the first tone of the second sub-block (shown as tone418) in accordance with the example data arrangement technique. Also, tone420is the third element of the first spreading pattern. Tone420is placed in the first tone of the third sub-block (shown as tone422). Remaining tones of spreading patterns of first data stream405may be placed in a similar manner. It is noted that the example data arrangement technique shown is for illustrative purposes only and that variations in the arrangement are possible. Therefore the discussion should not be construed as being limiting to either the scope or the spirit of the example embodiments.

According to an example embodiment, it may be possible to further exploit sparsity in the frequency domain present in a SCMA or LDS communications system. The pilot signals of a particular transmitting device may be transmitted according to a spreading pattern (e.g., SCMA codebook or LDS spreading signature) associated with the transmitting device. In other words, the pilot signals are transmitted at the same tones as the data transmitted by the transmitting device.

FIG. 5aillustrates example OFDM symbols500with pilot signals of a transmitting device placed in tones in accordance with a spreading pattern associated with the transmitting device. OFDM symbols500may be an example of OFDM symbols transmitted in a SCMA or LDS communications system. Pilot signals transmitted by transmitting devices are placed in tones of a time slot in accordance with spreading patterns (e.g., SCMA codebook or LDS spreading signatures) associated with the transmitting devices. As an illustrative example, OFDM symbols500includes pilot signals placed in sub-blocks 3 and 4 of time slot505with sub-blocks being numbered starting at 1 at the top of a time slot, corresponding to spreading pattern 0 0 1 1. It is noted that each of the sub-blocks corresponds to a group of contiguous tones.

FIG. 5billustrates example time slots550containing pilot signals transmitted by a plurality of transmitting devices with the pilot signals placed in tones in accordance with spreading pattern associated with the plurality of transmitting devices. Since the pilot signals transmitted by the plurality of transmitting devices occupy tones in accordance with the spreading patterns associated with the plurality of transmitting devices, mutual interference is reduced. As an illustrative example, consider sub-block555that includes pilot signals transmitted by UE1. It is noted that only sub-blocks560and565are also occupied by pilot signals transmitted by UE3and UE5. Therefore, only UE1, UE3, and UE5suffer mutual interference in the tone that corresponds to sub-blocks555,560, and565.

According to an example embodiment, it may not be necessary to estimate the channel corresponding to a tone where no data is being transmitted since, for a particular transmitting device, pilot signals are transmitted only on sub-blocks corresponding to tones that are also used to transmit data transmitted by the transmitting device. Hence, the transmit power level of the pilot tones may be increased. The increased transmit power level may result in better channel estimation performance as well as overall communications performance.

Frequency diversity may be achieved when a transmission is made in multiple frequency bands, e.g., tones, to improve the reliability of the delivery of the transmission. Frequency diversity is typically used to combat fading, interference, and the like. In general, frequency diversity uses a wider frequency bandwidth range to perform the transmission.

According to an example embodiment, the arrangement of the pilot signals and/or the data may be performed in a different manner to exploit frequency diversity. As an example, it may be possible to partition the available bandwidth of an OFDM symbol into multiple blocks and within each block, place the pilot signals and/or data in accordance with spreading patterns.

FIG. 6aillustrates example OFDM symbols600with a single partition. As shown inFIG. 6a, the data and pilot signals are transmitted according to spreading pattern 0 1 0 1. The bandwidth of OFDM symbols600may be partitioned into M=1 partitions. M may also be referred to as a diversity factor. In general, as M increases, the frequency diversity also increases. Pilot signals and/or data of transmissions made by transmitting devices may be placed in each partition of OFDM symbols600in accordance with spreading patterns associated with the transmitting devices. Since M=1, frequency diversity may not be achieved for all spreading patterns.

FIG. 6billustrates example OFDM symbols650with two partitions. As shown inFIG. 6b, the data and pilot signals are transmitted according to spreading pattern 0 1 0 1. The bandwidth of OFDM symbols650may be partitioned into M=2 partitions, a first partition655and a second partition660. Pilot signals and/or data of transmissions made by transmitting devices may be placed in each partition of OFDM symbols650in accordance with spreading patterns associated with the transmitting devices. Therefore, the pilot signals and/or data of transmissions may occur in each of the two partitions. The same arrangement technique may be used to place pilot signals and/or data in each partition or different arrangement techniques may be used for each partition. An optimum value for M (the number of partitions) may be determined for a variety of situations and stored at transmitting devices and receiving devices and may be selected depending on situation. Although the discussion illustrates the bandwidth of OFDM symbols being partitioned into 1 or 2 partitions, the example embodiments presented herein are operable for any number of partitions. Therefore, the discussion of 1 and 2 partitions should not be construed as being limiting to either the scope or spirit of the example embodiments.

An example data arrangement technique is as follows:a. Evenly partition the bandwidth of an OFDM symbol into M partitions;b. Within each partition, divide the partition into L (the length of a spreading pattern) sub-blocks;c. Starting with the first partition, put data (or pilot signals) into each partition byi. let xkdenote the k-th spreading pattern of the partition;ii. after spreading, xkis denoted by a vector of length L;iii. place the I-th (I=[1, . . . ,L]) element in the vector in the k-th tone of the I sub-block in the partition; andiv. when the partition is filled, go to the next block and set k=1.

A variation of the data arrangement technique may involve the transmitting device looping through the partitions instead of filling each partition completely prior to moving to the next partition.

The example embodiments discussed herein may be used in uplink transmissions and/or downlink transmissions. As an illustrative example, consider a situation where UE1is a cell-edge UE with spreading pattern 0 0 1 1.FIG. 7illustrates a diagram of stream700highlighting an example data arrangement technique for a downlink transmission. A first sequence705illustrates data after being spread by the spreading pattern 0 0 1 1. It is noted that the use of different spreading patterns will result in different sequences. A second sequence710illustrates the data after arrangement with the data arrangement technique.

FIG. 8illustrates a flow diagram of example operations800occurring in a receiving device as the receiving device receives OFDM symbols with pilot signals and/or data arranged in accordance with spreading patterns of transmitting devices. Operations800may be indicative of operations occurring in a receiving device, such as an eNB in an uplink transmission or a UE in a downlink transmission, as the receiving device receives OFDM symbols with pilot signals and/or data arranged in accordance with spreading patterns of transmitting devices.

Operations800may begin with the receiving device determining a spreading pattern SN for transmitting device N (block805). The spreading pattern SN may be assigned to transmitting device N when it initially powered on or attached with a communications system including the receiving device. The receiving device may determine a number of partitions M and a blocks configuration for the partitions (block810). The receiving device may determine the number of partitions M to optimize frequency diversity, as well as capability of the communicating devices (the transmitting device and the receiving device). The value of M may be pre-determined for a variety of situations and stored in the receiving device. The blocks configuration may specify how the bandwidth available is divided and the specific frequency ranges, tones, sub-blocks, and the like, belonging to each partition.

The receiving device may receive an OFDM symbol (block815). The receiving device may detect information associated with the transmitting device in accordance to the spreading pattern SN and the blocks configuration (block820). As an example, the receiving device may determine the location of the pilot signals of the transmitting device and the receiving device may detect the pilot signals at the locations and use the pilot signals for channel estimation. The channel estimates may be used by the receiving device to detect data transmitted by the transmitting device.

FIG. 9illustrates a flow diagram of example operations900occurring in a transmitting device as the transmitting device transmits OFDM symbols with pilot signals and/or data arranged in accordance with spreading patterns of transmitting device. Operations900may be indicative of operations occurring in a transmitting device, such as an eNB in a downlink transmission or a UE in an uplink transmission, as the transmitting device transmits OFDM symbols with pilot signals and/or data arranged in accordance with spreading pattern of transmitting device.

Operations900may begin with the transmitting device determining a spreading pattern SN for transmitting device N (block905). The spreading pattern SN may be assigned to transmitting device N when it initially powered on or attached with a communications system including the receiving device. The transmitting device may determine a number of partitions M and a blocks configuration for the partitions (block910). The transmitting device may determine the number of partitions M to optimize frequency diversity, as well as capability of the communicating devices (the transmitting device and the receiving device). The value of M may be pre-determined for a variety of situations and stored in the transmitting device. The blocks configuration may specify how the bandwidth available is divided and the specific frequency ranges, tones, sub-blocks, and the like, belonging to each partition. The transmitting device may partition the frequency range of the OFDM symbols into M partitions (block915).

The transmitting device may place information (pilot signals and/or data) in the OFDM symbol in accordance with the spreading pattern SN (block920). The transmitting device may utilize a data arrangement technique such as those disclosed herein to place the information in the OFDM symbol. The transmitting device may transmit the OFDM symbol (block925).

FIG. 10illustrates an example communications device1000. Communications device1000may be an implementation of a transmitting device, such as an eNB in a downlink transmission or a UE in an uplink transmission, or a receiving device, such as an eNB in an uplink transmission or a UE in a downlink transmission. Communications device1000may be used to implement various ones of the embodiments discussed herein. As shown inFIG. 10, a transmitter1005is configured to transmit packets, OFDM symbols, and the like. Communications device1000also includes a receiver1010that is configured to receive packets, OFDM symbols, and the like.

A pattern determining unit1020is configured to determine a spreading pattern, e.g., a SCMA codebook or LDS spreading signature, for a transmitting device or of a transmitting device. A partition managing unit1022is configured to determine a number of partitions M, as well as generate a blocks configuration for the bandwidth of an OFDM symbol according to the number of partitions M. An information placing unit1024is configured to place pilot signals and/or data in an OFDM symbol in accordance with a spreading pattern of a transmitting device and a blocks configuration. An information detecting unit1026is configured to detect pilot signals and/or data from a transmitting device in accordance with the spreading pattern of the spreading device and the blocks configuration of the OFDM symbol. A memory1030is configured to store spreading patterns, blocks configuration, number of partitions M, and the like.

The elements of communications device1000may be implemented as specific hardware logic blocks. In an alternative, the elements of communications device1000may be implemented as software executing in a processor, controller, application specific integrated circuit, or so on. In yet another alternative, the elements of communications device1000may be implemented as a combination of software and/or hardware.

As an example, receiver1010and transmitter1005may be implemented as a specific hardware block, while pattern determining unit1020, partition managing unit1022, information placing unit1024, and information detecting unit1026may be software modules executing in a microprocessor (such as processor1015) or a custom circuit or a custom compiled logic array of a field programmable logic array. Pattern determining unit1020, partition managing unit1022, information placing unit1024, and information detecting unit1026may be modules stored in memory1030.