WO2009093218A2

WO2009093218A2 - Sequential data retransmission on individual resource blocks

Info

Publication number: WO2009093218A2
Application number: PCT/IB2009/050288
Authority: WO
Inventors: Ni Ma; Xiaobo Zhang; Gang Wu; Bo Yang
Original assignee: Nxp B.V.
Priority date: 2008-01-25
Filing date: 2009-01-25
Publication date: 2009-07-30
Also published as: WO2009093218A3

Abstract

A system and method for retransmission of a data segment in a wireless communication system. The system includes a transmitter, a receiver, and a retransmission manager. The transmitter transmits a data segment over a plurality of resource blocks. The data segment includes a plurality of data packets. Each of the data packets corresponds to one of the resource blocks. The receiver receives the data segment from the transmitter and determines that the data segment is incorrectly received. The retransmission manager initiates the retransmission of the data segment in response to the determination that the data segment is incorrectly received. The transmitter retransmits each of the data packets individually in sequence using the resource blocks originally assigned to the data packets.

Description

SEQUENTIAL DATA RETRANSMISSION ON INDIVIDUAL RESOURCE

BLOCKS

Embodiments of the invention relate generally to wireless communications systems and, more particularly, to data retransmissions using resource blocks. The 3rd Generation Partnership Project (3GPP) was established to produce globally applicable technical specifications and technical reports for a 3rd generation mobile system based on evolved Global System for Mobile (GSM) communications core networks and the radio access technologies that they support (i.e., Universal Terrestrial Radio Access (UTRA) in both Frequency Division Duplex (FDD) and Time Division Duplex (TDD) modes). The scope was subsequently amended to include the maintenance and development of the GSM technical specifications and technical reports including evolved radio access technologies (e.g., General Packet Radio Service (GPRS) and Enhanced Data rates for GSM Evolution (EDGE)).

Hybrid Automatic Repeat Request (HARQ) is one of the technologies of the 3GPP Long Term Evolution (LTE) system for high throughput data transmission. To satisfy this demand, sufficient resource blocks (RBs) are allocated. Resource blocks are groups of consecutive orthogonal frequency- division multiplexing (OFDM) symbols in the time domain and consecutive subcarriers in the frequency domain. According to current specifications, if a transmission of one data segment fails, a HARQ retransmission mechanism is triggered with all allocated RBs occupied. However, it often occurs that only few data packets of the data segment on paralleled RBs are erroneously received. OFDM is a basic multi-access scheme to realize high-speed data transmission for 3GPP LTE cellular system. OFDM integrates several advanced technologies such as Adaptive Modulation and Coding (AMC), HARQ, and so forth. Conventionally, HARQ combines Automatic Repeat Request (ARQ) and Forward Error Correction (FEC) schemes to improve the data retransmission efficiency. Some preliminary descriptions of conventional 3GPP LTE downlink transmission schemes, ARQ, HARQ, etc. are described herein.

Fig. 1 depicts a conventional 3GPP LTE downlink transmission architecture 10. More specifically, Fig. 1 depicts a general frame structure and resource grid for the 3GPP LTE downlink transmission architecture 10. In the conventional 3GPP LTE downlink transmission architecture 10, the transmitted signal for a data segment 12 is carried by one or more RBs 14, which are made up of OFDM symbols and sub-carriers. As indicated in Fig. 1, one time slot contains several OFDM symbols, and each OFDM symbol is modulated by a cluster of orthogonal sub-carriers. A resource element 16 is the smallest time-frequency unit of a RB 14, containing one sub-carrier and lasting one symbol time. Each RB 14 is formed by multiple resource elements and, as described above, is defined as numbers of consecutive OFDM symbols in the time domain and numbers of consecutive subcarriers in the frequency domain. In current 3GPP LTE systems, one data segment 12 is carried by several RBs 14. The exact number of RBs 14 is determined by radio resource scheduling.

In communication systems, if a data transmission fails, the receiver notifies the transmitter to retransmit the data segment by using a Not- Acknowledgement (NAK) feedback signal. On the contrary, if the data transmission is successful, the receiver validates the transmission by using an Acknowledgement (ACK) feedback signal. This type of acknowledgement scheme is referred to as Automatic Repeat Request (ARQ). Fig. 2 illustrates a conventional ARQ method 20 for an ARQ communication procedure in a cellular system. In particular, the base station 22 (i.e., transmitter) transmits a data packet to the terminal 24 (i.e., receiver), without FEC. At block 26, the terminal 24 determines if the data packet is demodulated correctly. If the data packet is not demodulated correctly, then the terminal 24 sends a NAK feedback signal to the base station 22, and the base station retransmits the data packet, for example, without any change. Otherwise, if the data is demodulated correctly, then the terminal 24 sends an ACK feedback signal to the base station 22. The base station 22 then proceeds to send another data packet, without FEC, to the terminal 24.

Due to the potential for deteriorated channel characteristics in wireless communication systems, FEC is often adopted to guarantee data transmission validity. However, FEC depresses the transmission efficiency, to an extent. Additionally, the signaling reporting of the ARQ method 20, described above, for successful or unsuccessful transmissions is performed via higher layer communications (typically, the radio resource control (RRC) layer), resulting in long delays in the retransmission process. HARQ, which combines ARQ and FEC, partially addresses the problems in the retransmission process. Facing the fact that FEC is self-correctable, to a certain extent, HARQ can apparently improve the high-speed data transmission efficiency with the help of the ARQ mechanism. In fact, HARQ can be regarded as an implicit link adaptation technique, and link layer acknowledgements are measured for retransmission decisions instead of the traditional upper layer (i.e., RRC) decision regarding retransmission. Fig. 3 illustrates a conventional HARQ method 40 for a HARQ communication procedure in a cellular system. The illustrated HARQ method 40 is substantially similar to the ARQ method 20 described above, except that the HARQ method also uses FEC for the transmission and retransmission of the data packet from the base station 22 to the terminal 24.

Conventional implementations of HARQ can be divided into three categories, according to how to combine received data at the receiver side. These categories are referred to herein as HARQ-type I, HARQ-type II, and HARQ-type III.

Fig. 4A illustrates a conventional HARQ-type I coding structure 50. HARQ-type I uses cyclic redundancy check (CRC) and FEC. In other words, redundancy information, Q, is attached to the valid data, D. If the receiver can correctly receive the data segment, then there is no need for the retransmission process. Otherwise, the retransmission mechanism is triggered to guarantee data accuracy. Hence, the whole data segment, I(L, K), is retransmitted, and the previous erroneous data segment is discarded.

Fig. 4B illustrates a conventional HARQ-type II coding structure 60. HARQ-type II uses FEC information, P(I), in addition to the original data segment, I(L,K). If the data is retransmitted, then L bits of data, R, are attached to the original data segment, I(L, K), to make up the error-correcting codeword. For reference, the original data segment, I(L,K), is transmitted as the first codeword, CO, and the data segment with the additional L bits of data, R, is subsequently transmitted as the retransmission codeword, C1(2L, L). Hence, if the original data segment, I (L, K), is transmitted and correctly received, then the retransmission is needless. However, if the original data segment, I(L,K) is not correctly received, then the original data segment, I(L,K), is transmitted with the additional FEC information, P(I). The receiver combines the original data segment, I(L, K), and the additional FEC information, P(I), to correct the error and decode the original data segment, I(L, K). Compared with HARQ-type I, the HARQ-type II coding structure 60 retransmits the redundant information, P(I), every time and reserves the first transmitted data segment I(L, K).

The HARQ-type III coding structure (not shown), compared with the HARQ-type II coding structure 60, uses a version of the retransmitted redundant information, P(I), which is self-decodable. Thus, the data segment can be directly recovered from the retransmitted redundancy information, P(I). Among the three types of HARQ, HARQ-type I is the simplest implementation, while HARQ-type III is the most complicated. HARQ-type II and HARQ-type III are also referred to as Incremental Redundancy (IR) HARQ (IR-HARQ) schemes, since the redundant information, P(I), is retransmitted.

In the existing HARQ schemes, if the transmitter receives a NAK feedback signal, then the transmitter retransmits the data segment on all allocated RBs 14. However, typically few data packets occupying fractional allocated RBs need to be retransmitted. As a result, the current HARQ scheme inevitably wastes radio resource to some extent. Embodiments of a system are described. In one embodiment, the system is a system to retransmit a data segment. The system includes a transmitter, a receiver, and a retransmission manager. The transmitter transmits a data segment over a plurality of resource blocks. The data segment includes a plurality of data packets. Each of the data packets corresponds to one of the resource blocks. The receiver receives the data segment from the transmitter and determines that the data segment is incorrectly received. The retransmission manager initiates the retransmission of the data segment in response to the determination that the data segment is incorrectly received. The transmitter retransmits each of the data packets individually in sequence using the resource blocks originally assigned to the data packets. Other embodiments of the system are also described. Embodiments of an apparatus are also described. In one embodiment, the apparatus is a transmitter to retransmit data packets of a data segment. The apparatus includes a resource block manager, a retransmission manager, a data segment selector, and a resource block selector. The resource block manager identifies a plurality of resource blocks for an initial transmission of a data segment. The data segment includes a plurality of data packets. Each of the data packets corresponds to one of the resource blocks. The retransmission manager receives an indication from a receiver that the data segment is incorrectly received at the receiver. The data segment selector selects at least a subset of the plurality of data packets for individual, sequential retransmission to the receiver. The resource block selector selects the plurality of resource blocks from the initial transmission of the data segment for the retransmission of the plurality of data packets to the receiver. Other embodiments of the apparatus are also described. Embodiments of a method are also described. In one embodiment, the method is a method for retransmission of a data segment. The method includes transmitting the data segment to a receiver over a plurality of resource blocks. The data segment includes a plurality of data packets, and each of the data packets corresponds to one of the resource blocks. The method also includes receiving an indication from the receiver that the data segment is incorrectly received at the receiver. The method also includes initiating a retransmission of the data segment in response to the indication from the receiver. The retransmission includes retransmitting each of the data packets individually in sequence using the resource blocks originally assigned to the data packets. Other embodiments of the method are also described.

Other aspects and advantages of embodiments of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrated by way of example of the principles of the invention. Fig. 1 depicts a conventional 3GPP LTE downlink transmission architecture. Fig. 2 illustrates a conventional ARQ method for an ARQ communication procedure in a cellular system.

Fig. 3 depicts a conventional HARQ method for a HARQ communication procedure in a cellular system. Fig. 4A illustrates a conventional HARQ-type I coding structure. Fig. 4B illustrates a conventional HARQ-type II coding structure. Fig. 5 depicts a schematic block diagram of one embodiment of a wireless communications system that may implement a broadband multi-channel system. Fig. 6 illustrates a schematic block diagram of a more detailed embodiment of the transmission resource manager of the wireless communications system of Fig. 5. Fig. 7 illustrates a schematic block diagram of a more detailed embodiment of the user equipment of the wireless communications system of Fig. 5. Fig. 8 illustrates a schematic flow chart diagram of one embodiment of a method for retransmitting a data segment.

Throughout the description, similar reference numbers may be used to identify similar elements.

While many embodiments are described herein, at least some of the described embodiments facilitate the retransmission scheme to address the problems described above. In one embodiment, a transmitter sequentially retransmits data packets of an erroneously received data segment on allocated RBs, and a receiver makes a decision after each retransmitted RB whether or not the data segment is correctly received. As long as receiver correctly detects the data segment, the residual data packets on the other allocated RB are not retransmitted. In other words, when the initial data transmission fails, it may be unnecessary to retransmit the data packets of one data segment on all allocated RBs. Thus, embodiments of the retransmission scheme reduce the consumption of RBs. Consequently, radio resources are potentially conserved. Fig. 5 depicts a schematic block diagram of one embodiment of a wireless communications system 100 that may implement a broadband multichannel system. The illustrated wireless communications system 100 includes a base station 102, or an evolved Node B (eNB), and multiple mobile stations 104, or user equipment (UE). For description purposes, the eNB 102 also may be referred to generically as a transmitter, and the UE 104 may be referred to generically as a receiver. Alternatively, in some embodiments, the eNB 102 also may be referred to generically as the receiver, and the UE 104 may be referred to generically as the transmitter, depending on the direction of data communication within the wireless communications system 100. The wireless communications system 100 may be operated in various modes, including multi-user multiple-input multiple-output (MU-MIMO) mode.

In the illustrated embodiment, the eNB 102 includes four antennas 106, although the eNB 102 can include more than four antennas 106. The eNB 102 also includes a transmission resource manager 110. In general, the eNB 102 is responsible for managing transmission resources (i.e., resource blocks) of the wireless communications system 100. One example of the transmission resource manager 110 is shown in Fig. 6 and described in more detail below. In one embodiment, the UEs 104 are wireless communications mobile stations that support wireless operations as specified in the 3GPP LTE specification. The UEs 104 may have one or two antennas 108, although the UEs 104 are not limited to two antennas 108 (e.g., the UEs 104 can include more than two antennas 108). One example of the UE 104 is shown in Fig. 7 and described in more detail below. Other embodiments of the wireless communications system 100 may implement other wireless schemes for broadband multi-carrier systems such as WiMAX.

Fig. 6 illustrates a schematic block diagram of a more detailed embodiment of the transmission resource manager 110 of the wireless communications system 100 of Fig. 5. Although the depicted transmission resource manager 110 includes several functional blocks described herein, other embodiments of the transmission resource manager 110 may include fewer or more functional blocks to implement more or less functionality. The illustrated transmission resource manager 1 10 includes a resource block manager 112, an antenna manager 114, a transmission scheme manager 116, and a retransmission manager 1 18. The transmission scheme manager 1 10 is coupled to the eNB 102. In general, the transmission resource manager 1 10 facilitates allocation of radio resources such as RBs to the UE 104 based on channel status feedback from the UE 104. In one embodiment, the resource block manager 112 is responsible for identifying radio resources, or RBs, that are available for baseband transmission. In particular, the resource block manager 112 identifies at least one available frequency band within a downlink frequency band. Radio resources, or resource blocks, may refer to frequency blocks in the frequency domain and/or time blocks in the time domain.

In one embodiment, the antenna manager 114 is responsible for identifying antennas 106 of the eNB 102 that are available for baseband transmissions. Among other things, the antennas 106 transmit data using the allocated RBs to communicate the data to one or more UEs 104.

In one embodiment, the transmission scheme manager 116 is responsible for establishing a transmission scheme for the UEs 104. The transmission scheme defines both the allocation of available radio resources, or RBs, and the selection of available antennas 106 amongst the UEs 104. In some embodiments, the transmission scheme manager 116 facilitates allocation of radio resources to the UEs 104 based on channel status feedback from the UE 104.

In one embodiment, the eNB 102 acts as a transmitter to transmit a data segment over a plurality of RBs. As explained above, the data segment includes a plurality of data packets, and each data packet corresponds to one of the resource blocks. In this embodiment, the UE 104 acts as a receiver to receive the data segment from the eNB 102. The UE 104 also determines whether the data segment is correctly or incorrectly received. In other words, the UE 104 determines if any of the associated data packets contains errors. If the UE 104 determines that the data segment is incorrectly received, the retransmission manager 118 initiates a retransmission of the data segment, in which each of the data packets is individually retransmitted in sequence using the RBs originally assigned to the data packets. In this way, one or more of the data packets is retransmitted, one data packet at a time, using the originally allocated RBs. The retransmission manager 118 is also configured to terminate the retransmission of the data packets, prior to completion of the retransmission of all of the data packets, once the UE 104 determines that the data segment is correctly received. Thus, the retransmission manager 118 may terminate the retransmission after only some of the data packets are retransmitted.

The illustrated retransmission manager 118 includes a data segment selector 120, a resource block selector 122, and a retransmission sequencer 124. In one embodiment, the data segment selector 120 selects at least a subset of a plurality of data packets of the data segment for the retransmission to the UE 104. The resource block selector 122 selects corresponding RBs for the selected data packets of the data segment. In one embodiment, the resource block selector 122 selects the RBs which were originally assigned, or allocated, to each of the data packets during the initial transmission of the data segment. Fig. 7 illustrates a schematic block diagram of a more detailed embodiment of the UE 104 of the wireless communications system 100 of Fig. 5. Although the depicted UE 104 includes several functional blocks described herein, other embodiments of the UE 104 may include fewer or more functional blocks to implement more or less functionality.

The illustrated UE 104 includes a transmission verification manager 126 and a feedback generator 128. In general, the transmission verification manager 126 determines whether the data segment is incorrectly received. In one embodiment, the transmission verification manager 126 makes a determination whether or not the data segment is correctly received after all of the corresponding data packets are initially transmitted, and then again after each individual data packet is separately retransmitted. In other embodiments, the transmission verification manager 126 also may determine whether or not the data segment is correctly received at other times during the transmission process. The feedback generator 128 includes a non-acknowledgment (NAK) feedback generator 130 and an acknowledgment (ACK) feedback generator 132. The NAK feedback generator 130 generates a NAK feedback signal in response to a determination that the data segment is incorrectly received. In contrast, the ACK feedback generator 132 generates an ACK feedback signal in response to a determination that the data segment is correctly received.

It should also be noted that some embodiments of the UE 104 also may include a retransmission manager similar to the retransmission manager 118 of the transmission resource manager 110 of Fig. 6, as described above. By implementing a retransmission manager at the UE 104, the UE 104 may be capable of retransmitting one or more data packets, for example, in sequence using the originally allocated RBs from the UE 104 to the eNB 102, according to the retransmission scheme described above. In other words, the UE 104 may include a retransmission manager to implement a retransmission scheme during data communications in which the UE 104 acts as a transmitter and the eNB 102 acts as a receiver.

Fig. 8 illustrates a schematic flow chart diagram of one embodiment of a method 140 for retransmitting a data segment. Although the depicted retransmission method 140 is described in conjunction with the wireless communications system 100 of Fig. 5, some embodiments of the retransmission method 140 may be implemented in conjunction with other wireless communications systems.

In general, the illustrated retransmission method 140 relates to data communications between a base station (eNB) 102 and a terminal (UE) 104. To begin, the eNB 102 initially transmits the data packets of the data segment to the UE 104. In particular, each of the data packets is transmitted on a corresponding RB. As one example, four RBs are shown and labeled as RBl, RB2, RB3, and RB4. Other embodiments may use fewer or more RBs. Additionally, the labeling used herein for the RBs is merely exemplary and does not necessarily correspond to a particular order in which the corresponding data packets might be initially transmitted from the eNB 102 to the UE 104.

After the UE 104 receives the initial transmission of the data packets, at block 142 the transmission verification manager 126 determines whether the data segment is correctly received. If the data segment is not correctly received, then the feedback generator 128 invokes that NAK feedback generator 130 to send a NAK feedback signal to the eNB 102. In response to the NAK feedback signal, the eNB 102 initiates a retransmission of the data segment. More specifically, the eNB 102 retransmits each of the data packets individually in sequence using the RBs originally assigned to the data packets. As shown in Fig. 5, the eNB 102 retransmits a first data packet corresponding to RBl because, in one embodiment, RBl is the same RB that was initially used to transmit the first data packet. Alternatively, a different RB may be used to retransmit the first data packet. At block 144, the UE 104 detects the data segment using the retransmission of RBl. After the UE 104 receives the retransmitted data packet corresponding, for example, to RBl, then at block 146 the transmission verification manager 126 determines whether the data segment is correctly received, based on the retransmission of RBl. If the data segment is not correctly received after the retransmission of RBl, then the feedback generator 128 invokes the NAK feedback generator 130 to send a subsequent NAK feedback signal to the eNB 102. In response to the subsequent NAK feedback signal, the eNB 102 retransmits a second data packet corresponding to RB2. At block 148, the UE 104 detects the data segment using the retransmission of RB2. After the UE 104 receives the retransmitted data packet corresponding, for example, to RB2, then at block 150 the transmission verification manager 126 determines whether the data segment is correctly received, based on the retransmission of RB2. If the data segment is not correctly received after the retransmission of RB2, then the feedback generator 128 invokes the NAK feedback generator 130 to send another NAK feedback signal to the eNB 102. In response to the NAK feedback signal, the eNB 102 retransmits a third data packet corresponding to RB3. At block 152, the UE 104 detects the data segment using the retransmission of RB3. After the UE 104 receives the retransmitted data packet corresponding, for example, to RB3, then at block 154 the transmission verification manager 126 determines whether the data segment is correctly received, based on the retransmission of RB3. If the data segment is not correctly received after the retransmission of RB3, then the feedback generator 128 invokes the NAK feedback generator 130 to send another NAK feedback signal to the eNB 102. In response to the NAK feedback signal, the eNB 102 retransmits a fourth data packet corresponding to RB4.

At block 156, the UE 104 detects the data segment using the retransmission of RB4. After the UE 104 receives the retransmitted data packet corresponding, for example, to RB4, then at block 158 the transmission verification manager 126 determines whether the data segment is correctly received, based on the retransmission of RB4. If the data segment is not correctly received after the retransmission of RB4, then the feedback generator 128 invokes the NAK feedback generator 130 to send another NAK feedback signal to the eNB 102 and, since all of the data packets have been retransmitted, the eNB 102 initiates another retransmission sequence starting with RBl.

Otherwise, if the data segment is correctly received after the retransmission of RB4, then the feedback generator 128 invokes the ACK feedback generator 132 to send an ACK feedback signal to the eNB 102.

Likewise, if the data segment is correctly received after the retransmission of any of RBl, RB2, or RB3, then the feedback generator 128 invokes the ACK feedback generator 132 to send an ACK feedback signal to the eNB 102. After the eNB 102 receives an ACK feedback signal from the UE 104, the eNB 102 may start transmitting a new data segment. The illustrated retransmission method 140 then ends.

Hence, according to the exemplary retransmission method 140 described above, the UE 104 notifies the eNB 102 to retransmit by sending a NAK feedback signal. The eNB 102 repeatedly retransmits the data packet in sequence until the data segment is correctly received. During the retransmission, the data packets on respective designated RBs are retransmitted one by one, according to a pre- assigned RB sequence. The pre-assigned RB sequence may be the same as or different from the original RB sequence used during the initial transmission of the data segment.

In contrast, if the data segment is correctly received, then the UE 104 acknowledges transmission validity by sending an ACK feedback signal to the eNB 102. The ACK feedback signal is used to notify the eNB 102 to not retransmit the residual data packets.

It should also be noted that the roles of the eNB 102 as a transmitter and the UE 104 as the receiver may be reversed, in other embodiments, so that the UE 104 retransmits data packets to the eNB 102. In some embodiments, the eNB 102 and the UE 104 alternatively function as the transmitter and the receiver, depending on the direction of the data communications.

Embodiments of the retransmission scheme described above facilitate reduced traffic load by sequentially retransmitting data packets partitioned from the data segment on respectively allocated RBs. Additionally, embodiments of the retransmission scheme achieve radio resource savings because only one sub- carrier or RB at a time is used for retransmission with the remainder available for other transmission services during each retransmission procedure.

Some embodiments of the retransmission scheme may introduce delay because data packets are retransmitted one by one, compared with conventional retransmission procedures which simultaneous retransmit all the data packets. Implementations of the wireless communications system 100 may be insensitive to such delay, though, based on the intrinsic Selective Repeat (SR) function of HARQ. Additionally, embodiments of the retransmission scheme can reduce the total retransmission time, to some extent, thus rendering any introduced delay negligible for the system as a whole.

In addition to the embodiments described above, it may be helpful to review some statistical analysis for an exemplary retransmission scheme, in comparison with a conventional retransmission scheme. For convenience, the following statistical analysis assumes that there are four RBs bearing one data segment, similar to the RBs shown in Fig. 8. Additionally, for ease of explanation, it is also assumed that the retransmission corresponding to the data segment is successful only once, and every sub-carrier or RB is independent and has equal erroneous probability, P , during transmission. Also, the mathematical

C^r P^r operations ⁿ and ⁿ denote combination and permutation operations, respectively. Let:

P ^{current scheme} ^_{6 me erroneous} probability corresponding to a data segment during one frame for the current scheme, c^urrent __S ^cheme fø _{me num}ber of occupied RBs during one frame for the current retransmission scheme, whose mathematical expectation is

,

P pr^op^osed _^sch^em^{e, t} b_{e me erroneous} probability corresponding to a data segment during one frame for the proposed scheme, wherein the transmission is wrong on ^{ RBs and that is correct on the other

4 ^" ' RBs, m proposed _scheme,t tøg _{me num}b_er of occupied RBs during one frame for the proposed retransmission scheme, wherein the transmission is wrong on t RBs and that is correct on the other 4 - 1 RBs_; and whose mathematical expectation is Ψ¹ pr^op^osed _^sch^em^e ) _{; and}

' ' be the emergency probability during one frame wherein there are totally t erroneous RBs, among which the last one is the ' RB. Based on the above assumptions, (l — p) is the correct probability corresponding to one RB during one frame. Further, the probability of correctly transmitting the whole data segment is (l - pf within the same time. Thus, the retransmission probability of the current scheme during one frame is given by:

— 1 (λ Y

± current scheme V ± }

According to conventional retransmission schemes, as long as the transmission fails, four RBs are all in use for retransmission. Thus, the mathematical expectation of occupied RBs, namely ^ ^current -^scheme\ is equal to the number of retransmitted RBs during one frame, that is:

^ \^m 'current scheme ) ^{= m} current scheme = 4(1 — (1 — /?) J

With respect to the proposed retransmission scheme, if ^ ^{~ ~} > is assumed as the number of RBs used when the transmission fails, the retransmission probability corresponding to a data segment during one frame is given by:

P proposed scheme,!

^~ P) J

Apparently, the number of occupied RBs for the proposed retransmission scheme depends on the various set of erroneous RBs, as well as the retransmission probability. That is to say, a different set of erroneous RBs affects the statistical number of RBs occupied for retransmission. To describe more explicitly, suppose that there is only one erroneous sub-carrier or RB. In that case, if it is the first sub-carrier or RB is the erroneous one, the retransmission process can be accomplished by only retransmitting the first part of the data segment. If, however, it is the second sub-carrier or RB that is the erroneous one, the retransmission process is evaluated based on both the second sub-carrier or RB and also the previous one. Similarly, other cases can be easily concluded and, hence, the actual number of employed RBs is statistically derived by summing up the number of RBs corresponding to all of the possible cases, as mentioned above, and calculating the average as a result.

For example, if one sub-carrier or RB is wrong and the other 3 RBs are right, i.e., ^{t =} 1 , whichever RB includes the error, wherein ^>l ^ ' ' ' ' is

equal, i.e., P ⁴⁴. Accordingly, the number of totally consumed sub-carrier or RBs is the sum of all the possible cases, that is:

m proposed _ sc heme, 1 Jr proposed _scheme, 1 ^ ^V^ ('**,,)

= C>(l-p)³x(lx^ P,³ + 2 „x^ P,³ ₊ „ 3x^ P,³ ₊ 4.x^ P,³)

P * 4⁴ P ¹4⁴ P ¹4

= \0p{\-p)³

If two RBs are wrong and the other 2 RBs are right, i.e., ^{t =} 2 , at least two RBs are consumed for retransmission. Here:

so the number of totally occupied RBs is given by:

m_p ψ_ιoposed _scheme, 2 P proposed _scheme, 2 / _* \ Hι,t J ι=t p³r^l p; P; P;

If three RBs are wrong and the other 1 code channel is right, i.e., ^{{ =} 3 , at least three RBs are consumed for retransmission. Here:

so the number of totally occupied RBs is given by:

If four RBs all transfers in error, i.e., ^{t =} ^ , then all RBs are occupied for retransmission. Here:

so the number of occupied RBs is given by:

^4

= 4/

If quantitative frames are transmitted, the mathematic expectation of occupied RBs for the proposed retransmission is given by

^EΨ proposed _sche_me ) = Σ ™ proposed _sche_me, , = ^~ / + ^P' ^~ ^P² + ^P t=\ Comparing the two mathematical expressions gives:

^E(m_{current scheme} )- E(m_{proposed scheme}) = -3 p⁴ + Up³ - Hp¹ + βp

:- 0 < p ≤ l :. - p(p -l)(3p² -%p + 6) > 0

Hence:

^ V"* proposed scheme ' ^ ^- ' V" current scheme )

This explains that the occupied RBs for retransmission in embodiments of the proposed retransmission scheme are statistically decreased so that more residual RBs can be available to other transmission services. Based on this comparison, embodiments of the proposed retransmission scheme can effectively conserve radio resources. It should be noted that, although only the case of four RBs is considered above, the procedure of mathematical deduction above can be extended to the case of any number, n , of RBs and the same or a similar conclusion can be derived.

Hence, embodiment of the proposed retransmission scheme can eliminate the need to retransmit the whole data segment on all allocated RBs. Some embodiments retransmit the data packets one at a time on a sub-carrier or RB in the sequence of RBs. Also, in some embodiments, after every retransmission is received, the detection decision may be made to decide whether or not the next data packet will be retransmitted. If a data packet is retransmitted, then only one RB is in use at a time for retransmission, and the other RBs may be used for other transmission services.

Embodiments of the proposed retransmission scheme can be applied to various wireless communication systems, including cellular systems which employ HARQ technique (e.g., 3GPP R6 & R7, 3GPP LTE and WiMAX, etc.). Additionally, embodiments of the proposed retransmission scheme may be effective in the case of severely obstructed channels. Although the operations of the method(s) herein are shown and described in a particular order, the order of the operations of each method may be altered so that certain operations may be performed in an inverse order or so that certain operations may be performed, at least in part, concurrently with other operations. In another embodiment, instructions or sub-operations of distinct operations may be implemented in an intermittent and/or alternating manner.

Although specific embodiments of the invention have been described and illustrated, the invention is not to be limited to the specific forms or arrangements of parts so described and illustrated. The scope of the invention is to be defined by the claims appended hereto and their equivalents.

Claims

What is claimed is:

1. A method for retransmission of a data segment, the method comprising: transmitting the data segment to a receiver over a plurality of resource blocks, wherein the data segment comprises a plurality of data packets, and each of the data packets corresponds to one of the resource blocks; receiving an indication from the receiver that the data segment is incorrectly received at the receiver; and initiating a retransmission of the data segment in response to the indication from the receiver, wherein the retransmission comprises retransmitting each of the data packets individually in sequence using the resource blocks originally assigned to the data packets.

2. The method of claim 1, further comprising: receiving an acknowledgment signal from the receiver to indicate that the data segment is correctly received at the receiver; and terminating the retransmission of the data segment, in response to the acknowledgment signal from the receiver, prior to completing the retransmission of all of the data packets of the data segment.

3. The method of claim 1, further comprising monitoring for a feedback signal from the receiver after retransmitting a first data packet and prior to retransmitting a second data packet.

4. The method of claim 1, further comprising: transmitting the data packets of the data segment according to a transmission sequence during the initial transmission of the data segment to the receiver; and retransmitting the data packets of the data segment according to a retransmission sequence during the retransmission of the data segment to the receiver, wherein the retransmission sequence is the same as the transmission sequence.

5. The method of claim 1, wherein each of the resource blocks comprises a number of consecutive OFDM symbols in time domain format and a number of consecutive subcarriers in frequency domain format.

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6. The method of claim 1, further comprising: receiving the transmission of the data segment at the receiver; determining that the data segment is incorrectly received at the receiver; generating the indication that the data segment is incorrectly received at the receiver; and sending the indication to the transmitter.

7. The method of claim 1, further comprising: detecting each data packet retransmission at the receiver; and determining, after each data packet retransmission, whether the data segment is correctly received at the receiver.

8. The method of claim 7, further comprising: determining that the data segment, including at least one data packet retransmission, is incorrectly received at the receiver; generating a subsequent indication that the data segment is incorrectly received at the receiver; and sending the subsequent indication to the transmitter.

9. The method of claim 7, further comprising: determining at the receiver that the data segment is correctly received at the receiver; generating an acknowledgment signal to indicate the data segment is correctly received at the receiver; and sending the acknowledgment signal to the transmitter.

10. A system to retransmit a data segment, the system comprising: a transmitter to transmit the data segment over a plurality of resource blocks, wherein the data segment comprises a plurality of data packets, and each of the data packets corresponds to one of the resource blocks; a receiver to receive the data segment from the transmitter and to determine that the data segment is incorrectly received; and a retransmission manager coupled to the transmitter, the retransmission manager to initiate a retransmission of the data segment in response to the determination that the data segment is incorrectly received, wherein the transmitter is further configured to retransmit each of the data packets individually in sequence using the resource blocks originally assigned to the data packets.

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11. The system of claim 10, wherein the retransmission manager is further configured to terminate the retransmission of the plurality of data packets prior to completion of the retransmission of the plurality of data packets.

12. The system of claim 10, wherein the transmitter comprises a data segment selector coupled to the retransmission manager, the data segment selector to select at least a subset of the plurality of data packets for the retransmission to the receiver.

13. The system of claim 12, wherein the transmitter further comprises a resource block selector coupled to the retransmission manager, the resource block selector to select the resource blocks originally assigned to each of the data packets for use in the retransmission of the corresponding data packets.

14. The system of claim 13, wherein the transmitter further comprises a retransmission sequencer coupled to the retransmission manager, the retransmission sequencer to schedule the individual retransmission of each of the plurality of data packets.

15. The system of claim 10, wherein the receiver comprises a transmission verification manager to determine whether the data segment is incorrectly received.

16. The system of claim 15, wherein the receiver further comprises a feedback generator coupled to the transmission verification manager, the feedback generator comprising: a Not-Acknowledgment (NAK) feedback generator to generate a NAK feedback signal in response to a determination that the data segment is incorrectly received; and an Acknowledgment (ACK) feedback generator to generate an ACK feedback signal in response to a determination that the data segment is correctly received.

17. A transmitter to retransmit data packets of a data segment, the transmitter comprising: a resource block manager to identify a plurality of resource blocks for an initial transmission of a data segment, wherein the data segment comprises a plurality of data packets, and each of the data packets corresponds to one of the resource blocks;

22 a retransmission manager coupled to the resource block manager, the retransmission manager to receive an indication from a receiver that the data segment is incorrectly received at the receiver; a data segment selector coupled to the retransmission manager, the data segment selector to select at least a subset of the plurality of data packets for individual, sequential retransmission to the receiver; and a resource block selector coupled to the retransmission manager, the resource block selector to select the plurality of resource blocks from the initial transmission of the data segment for the retransmission of the plurality of data packets to the receiver.

18. The transmitter of claim 17, wherein the retransmission manager is further configured to terminate the retransmission of the plurality of data packets prior to completion of the retransmission of the plurality of data packets.

19. The transmitter of claim 17, further comprising a retransmission sequencer coupled to the retransmission manager, the retransmission sequencer to schedule the retransmission of the plurality of data packets according to the transmission sequence of the initial transmission of the data segment to the receiver.

20. The transmitter of claim 17, further comprising a retransmission sequencer coupled to the retransmission manager, the retransmission sequencer to schedule the retransmission of the plurality of data packets according to a retransmission sequence which is different from a transmission sequence of the initial transmission of the data segment to the receiver.

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