A cellular communications network typically includes a variety of communication nodes coupled by wireless or wired connections and accessed through different types of communications channels. Each of the communication nodes includes a protocol stack that processes the data transmitted and received over the communications channels. Depending on the type of communications system, the operation and configuration of the various communication nodes can differ and are often referred to by different names. Such communications systems include, for example, a Code Division Multiple Access 2000 (CDMA2000) system and a Universal Mobile Telecommunications System (UMTS).
Third generation wireless communication protocol standards (e.g., 3GPP-UMTS, 3GPP2-CDMA2000, etc.) may employ a dedicated traffic channel in the uplink (e.g., a communication flow between a mobile station (MS) or User Equipment (UE), hereinafter referred to as a user, and a base station (BS) or NodeB). The dedicated channel may include a data part (e.g., a dedicated physical data channel (DPDCH) in accordance with UMTS Release 4/5 protocols, a fundamental channel or supplemental channel in accordance with CDMA2000 protocols, etc.) and a control part (e.g., a dedicated physical control channel (DPCCH) in accordance with UMTS Release 4/5 protocols, a pilot/power control sub-channel in accordance with CDMA2000 protocols, etc.).
Newer versions of these standards, for example, Release 6 of UMTS provide for high data rate uplink channels referred to as enhanced dedicated channels (E-DCHs). An E-DCH may include an enhanced data part (e.g., an E-DCH dedicated physical data channel (E-DPDCH) in accordance with UMTS protocols) and an enhanced control part (e.g., an E-DCH dedicated physical control channel (E-DPCCH) in accordance with UMTS protocols).
FIG. 1 illustrates a conventional wireless communication system 100 operating in accordance with UMTS protocols. Referring to FIG. 1, the wireless communication system 100 may include a number of NodeBs such as NodeBs 120, 122 and 124, each serving the communication needs of a first type of user 110 and a second type of user 105 in their respective coverage area. The first type of user 110 may be a higher data rate user such as a UMTS Release 6 user, referred to hereinafter as an enhanced user. The second type of user may be a lower data rate user such as a UMTS Release 4/5 user, referred to hereinafter as a legacy user. The NodeBs are connected to an RNC such as RNCs 130 and 132, and the RNCs are connected to a MSC/SGSN 140. The RNC handles certain call and data handling functions, such as, autonomously managing handovers without involving MSCs and SGSNs. The MSC/SGSN 140 handles routing calls and/or data to other elements (e.g., RNCs 130/132 and NodeBs 120/122/124) in the network or to an external network. Further illustrated in FIG. 1 are interfaces Uu, Iub, Iur and Iu between these elements.
An example of a frame structure for the E-DCHs (e.g., E-DPCCH and E-DPDCH) in the uplink direction is illustrated in FIG. 2. Each frame 200 may have a length of, for example, 10 milliseconds (ms) and may be partitioned into 5 sub-frames each including 3 slots. Each slot 205 may have a length of, for example, 2560 chips, and may have a duration of, for example, 2/3 ms. Consequently, each sub-frame may have a duration of 2 ms.
As discussed above, an E-DCH includes an E-DPDCH 240 and an E-DPCCH 220, and each of the E-DPCCH 220 and the E-DPDCH 240 may be code multiplexed.
The E-DPCCH 220 carries control information for an associated E-DPDCH 240. This control information includes three components: a re-transmission sequence number (RSN), a transport format indicator (TFI) and a happy bit. The RSN indicates the transmission index of an associated packet transmitted on the E-DPDCH. That is, the RSN value indicates the number of times data associated with an upper layer enhanced dedicated transport channel (E-DTrCH), and associated control information has been transmitted by a UE without receiving an acknowledgment (ACK) from the NodeB in return. Currently in UMTS Release 6, the RSN has a maximum value of 3 and is represented by two bits.
The TFI indicates the data format for the transport channel carried by the associated E-DPDCH (e.g., transport block size, transmission time interval (TTI), etc.) and is represented by 7 bits. The TFI value may be a value selected from a transport format set (TFS) including all possible TFI values for a given transmission.
The happy bit is a binary indicator, which may be used by a UE to inform one or more NodeBs whether the UE is satisfied with the current setup of the E-DCH channels and is represented by a single bit. For example, UE 110 of FIG. 1 may use this indicator to inform one of the NodeBs 120/122/124 that the UE 110 can handle greater data capacity. In other words, the happy bit is a rate increase request bit.
FIG. 3 illustrates a conventional UMTS uplink transmitter 300 located at the enhanced UE 110 of FIG. 1 and a receiver 350 located at one of the NodeBs 120/122/124. The conventional transmitter 300 and receiver 350 of FIG. 3 may transmit and receive E-DCHs.
As shown in FIG. 3, data associated with an upper layer enhanced dedicated transport channel (E-DTrCH) may be processed into E-DPDCH frames at the transmission channel processing block 303. The frames may be binary phase shift keying (BPSK) modulated and orthogonally spread at the modulation and orthogonal spreading unit 304. The spread modulated frames are received by the gain unit 315 where an amplitude of the spread modulated frames may be adjusted. A combiner 320 receives the output of the gain unit 315.
Still referring to FIG. 3, the 2 RSN bits, the 7 TFI bits and the 1 happy bit are mapped into a 10-bit E-DPCCH word, which may be control information for an associated E-DPDCH frame having a TTI of, for example, 2 ms or 10 ms.
The 10-bit E-DPCCH word includes a happy bit set to a given value (e.g., ‘1’ or ‘0’), a format indicator or TFI having a value corresponding to a data format for the transport channel carried by the associated E-DPDCH frame (e.g., transport block size, transmission time interval (TTI), etc.), and an RSN value between 0 and 3. The happy bit and the TFI may be referred to as control data.
The 10-bit E-DPCCH word may then be coded into a 30-bit coded sequence at an FEC unit 301. That is, for example, the 10-bit E-DPCCH word associated with a single E-DPDCH frame is first coded into a 32-bit E-DPCCH codeword using a (32, 10) sub-code of the second order Reed-Muller code. The 32-bit codeword is then punctured to (30, 10) code to generate the 30 coded symbols (in this case 1 bit will represent 1 symbol) to be transmitted. These 30 coded symbols are transmitted in one sub-frame; for example, 3 slots 200 as shown in FIG. 2 with 10-bits per slot.
Returning to FIG. 3, the 30-bit coded sequence is modulated at a BPSK Modulator 305 and orthogonally spread at an orthogonal spreading unit 310. The output from the orthogonal spreading unit 310 is gain adjusted at a gain unit 316 and output to the combiner 320.
Similar to the above E-DPCCH, well-known DPCCH frames used in determining, for example, channel estimates, are modulated at a BPSK Modulator 306, and the modulated frames are orthogonally spread at an orthogonal spreading unit 311. The spread modulated frames are received by a gain unit 317 where an amplitude of the spread modulated frames may be adjusted.
The outputs of each of the gain units 315, 316 and 317 are complex signals and are combined (e.g., code-division and/or I/Q multiplexed) into a combined signal by a combiner unit 320. The combined signal is scrambled and filtered by a shaping filter 325, and the output of the shaping filter 325 is sent to the receiver 350 via a propagation channel 330 (e.g., over the air).
After the transmitter 300 transmits the combined signal over the propagation channel 330, the transmitting UE awaits an ACK from the NodeB indicating that the transmitted signal has been successfully received and decoded.
If an ACK is received by the user, the transmitter 300 may transmit new E-DTrCH data. If an ACK is not received or an NACK is received, the UE may retransmit data from the same E-DTrCH and similar control information via an E-DPDCH frame and corresponding E-DPCCH frame, respectively.
The retransmitted E-DPCCH frame includes the same or different happy bit value, the same TFI value, and an incremented RSN value. For example, if the RSN value of the initial frame is N, the RSN value of the retransmitted frame is N+1. Thus, RSN values for consecutive retransmissions of the same data are correlated in that the values are incremented by one.
After retransmitting the data and associated control information (e.g., via an E-DPDCH frame and a corresponding E-DPCCH frame, respectively) including an RSN value of N+1, if still no ACK is received from the NodeB or a NACK is received, the UE may retransmit the data and similar control information again via another E-DPDCH frame and E-DPCCH frame, respectively. In this retransmission (e.g., third transmission), the E-DPCCH frame may have an RSN value of N+2. The UE may continue to retransmit the non-acknowledged data until an ACK is received, or the number of retransmissions reaches a threshold value.
At the receiver 350, the transmitted signal is received over the propagation channel 330, and input to the E-DPDCH processing block 335, E-DPCCH soft-symbol generation block 345 and a DPCCH channel estimation block 355. As is well-known in the art, the DPCCH channel estimation block 355 generates channel estimates using pilots transmitted on the DPCCH. The channel estimates may be generated in any well-known manner, and will not be discussed further herein for the sake of brevity. The channel estimates generated in the DPCCH channel estimation block 355 may be output to each of the E-DPDCH processing block 335 and the E-DPCCH soft-symbol generation block 345.
At the soft-symbol generation block 345, the received control signal may be de-scrambled, de-spread, and de-rotated/de-multiplexed to generate a sequence of soft-symbols. The E-DPCCH soft-symbols may represent an estimate of the received signal, or in other words, an estimate of the 30 symbols transmitted by the transmitter 300. The E-DPCCH soft-symbols may be further processed to recover the transmitted E-DPCCH word.
The E-DPCCH soft-symbols are output to an E-DPCCH discontinuous transmission (DTX) detection unit 365. The E-DPCCH DTX detection unit 365 determines whether the signal received on the E-DPCCH is actually present using a thresholding operation.
For example, the E-DPCCH DTX detection unit 365 may normalize a signal energy for a received E-DPCCH frame (e.g., the signal energy over a given TTI of 2 ms) and compare the normalized signal energy to a threshold. If the normalized signal energy is larger than the threshold, the E-DPCCH DTX detection unit 365 determines that a control signal is present on the E-DPCCH; otherwise, the E-DPCCH DTX detection unit 365 determines that a control signal is not present on the E-DPCCH and, subsequently, declares a discontinuous transmission.
If the E-DPCCH DTX detection unit 365 detects that a control signal is present on the E-DPCCH, the soft-symbols output from the soft-symbol generation block 345 are processed by the E-DPCCH decoding block 375 to recover (e.g., estimate) the 10-bit E-DPCCH word transmitted by the transmitter 300.
For example, in recovering the transmitted 10-bit E-DPCCH word, the E-DPCCH decoding block 375 may determine a correlation value or correlation distance, hereinafter referred to as a correlation, between the sequence of soft-symbols and each 30-bit codeword in a subset (e.g., 2, 4, 8, 16, 32, etc.) of all 1024 possible E-DPCCH codewords that may have been transmitted by the transmitter 300. This subset of codewords may be referred to as a codebook.
After determining a correlation between the sequence of soft-symbols and each of the codewords in the codebook, the E-DPCCH decoding block 375 selects the 10-bit E-DPCCH word corresponding to the 30-bit E-DPCCH codeword, which has the highest correlation to the E-DPCCH soft-symbols. The 10-bit E-DPCCH word is then output to the E-DPDCH processing block 335 for use in processing the E-DPDCH.
If the E-DPDCH is successfully received and decoded at the receiver 350, the NodeB transmits an ACK to the transmitting UE in the downlink; otherwise, the NodeB transmits a NACK (e.g., if the NodeB is a serving NodeB) or nothing (e.g., if the NodeB is a non-serving NodeB)
The conventional E-DPCCH processing as shown in FIG. 3 is used to generate E-DPCCH performance results and/or set conformance test requirements for Release 6 UMTS standards. However, in conventional single-frame E-DPCCH processing, a high transmit power of E-DPCCH is required to achieve satisfactory detection performance. Moreover, performance does not improve as the number of retransmissions increases.
The E-DPCCH is decoded based on a single frame at all times. This limits the performance for the E-DPDCH, and results in faster power consumption and/or higher interference to other users.