Invented by Chengjun SUN, Yujian Zhang, Chunying Sun, Xiaoquiang Li, Ju-Ho Lee, Beijing Samsung Telecom R&D Center, Samsung Electronics Co Ltd
The Beijing Samsung Telecom R&D Center, Samsung Electronics Co Ltd invention works as followsThe invention discloses a method for determining a CQI_difference based on the CQI values of the CQI-reporting frequency subbands of the whole frequency band. If a condition is met, the UE will send the CQI_difference to the BS. The BS can then choose a better data transmission mode based on the measurement report that the UE sent to it.
Background for Methods and apparatus for measuring report for decision of transmission mode switch
The present invention is a radio communication device with localized data and distributed data modes, and in particular a method to create a measurement report for determining conversion of transmission mode.
The 3GPP standardization group has begun work on the Long-term Evolution of existing system criteria. OFDM (Orthogonal Frequency Division Multiplexing), among many physical layer transmission technologies, has become a major challenge for all downlink solutions due to its advantages, such as higher spectrum usage efficiency and lower processing complex.
OFDM is a multicarrier modulation technique. Its basic principle is the division of a high-rate data stream into several low-rate data streams for transmission via a grouping of orthogonal subcarriers at once. The OFDM technique is superior in many ways because of its multi-carrier features.
An excellent example of the superiority of OFDM is that Inter-Symbol Interference can be eliminated completely when the channel delay is smaller than the length a Cyclic prefix (CP), introduced by adding guard spacing between each symbol) because data is transmitted in parallel through multiple sub-carriers and the symbol length in each sub-carrier increases correspondingly without sensitivity to the channel delay. Each sub-carrier is then exposed to a flat fading. A complete OFDM symbol is made up of an OFDM signal that’s available and a prefix. The implementation of CP here is achieved by copying samples from the back of an available OFDM to the front.
The OFDM technology also has a high efficiency in spectrum utilization. OFDM signals actually overlap in the frequency domain. The overlap increases spectrum efficiency to a great extent.
The OFDM technique is also very effective in resisting narrowband interference and frequency selective fading. By channel coding, and interleaving the OFDM can achieve the frequency diversity and time diversity effects. This can effectively resist either narrowband interference and frequency selective fading.
Another remarkable advantage of the OFDM technology is the fact that modulation can be achieved through a base band Inverse Fast Fourier Transform. IFFT/FFT provides a fast calculation method, and can easily be implemented in a Digital Signal Processing chip and hardware structure.
There are two types of transmission in the OFDM radio system: localized transmission and distributed transmission.
The localized data transmitting means that data is transmitted sequentially in sub-carriers within the localized subband. The network entity will specify an effective modulation and coding for its data transmission, to achieve adaptive modulation coding based upon channel quality between a base station (BS) and user equipment (UE), thereby increasing data transmission throughput. Distributed transmission mode is when the UE transmits over the entire frequency band using comb-like carriers. This maximizes the frequency diversity gain by distributing the sub-carriers transmitting data as widely as possible. Localized data transmission modes that can make use of adaptive modulation and frequency scheduling have a higher transmission gain. Localized transmission can be difficult to implement for channels that change rapidly. Channel conditions predicted one time may not reflect the channel conditions of the next. This condition is commonly used for distributed data transmission to transmit data using frequency diversity gain.
The process of downlink data transmission is described.
For a localized mode of transmission, a UE measures the channel quality in each subband within the system frequency band and reports the measured Channel-Quality-Indicator (CQI), for each subband, to the BS. The BS will determine, based on the CQIs received from the UEs and the current system load, whether or not to allocate frequencies to UEs and what localized frequency bands they can use for data transmission. During data transmission, the UE must continue to measure channel quality in each sub-band of the system frequency band. It will then transmit the measured CQI back to the basestation to achieve the frequency scheduling goals and Adaptive modulation Coding (AMC). This will allow for maximum data transmission throughput.
For a distributed transmit mode, the UE measures the mean channel-quality of the entire system’s frequency band and then reports the average CQI value to the base station. The BS will then decide whether or not to distribute frequency resources to each UE based on the CQI reported by each UE, and the current system load. During data transmission, the UE must continue to measure the CQI average of the entire system band and send the measured CQI back to the basestation in order to achieve the frequency scheduling goals and the Adaptive modulation Coding (AMC). This allows for maximum data transmission throughput.
The descriptions show that the UE sends only the average CQI when it is in distributed transmission mode. The number of bits required to transmit CQI data in localized transmission is much greater than in distributed transmission.
The system will choose the appropriate data transmission mode between the BS/UE based on their channel conditions. When the channel conditions between the BS & UE change, the conversion from localized transmission to distributed transmission is likely to occur. IEEE 802.16E uses OFDM transmission in its radio transmission technology specification. It is likely that the transition will occur during the data transfer process. The conversion process is as follows. The conversion process for a distributed transmission to a localized mode is as follows. The UE will transmit a transition request to the BS and CQIs for 5 sub-bands that have the best channel quality if, within a certain time period, the maximum standard deviation of Signal to Noise Radio in time domain measured across all frequency bands is less than a predefined threshold and the mean SNR in the entire frequency band is greater than the threshold value. The BS will then specify the sub-bands the UE can use, and the adaptive modulation coding based upon the channel quality of several sub-bands reported by the UE. The UE can then change its data transmission mode to localized transmission by requesting the BS.
The conversion from a localized to distributed transmission mode is done as follows: The UE will send a request to switch from localized to distributed mode if the standard deviation in SNRs for all frequency subbands is greater than a threshold value. It will also send the channel quality in the entire frequency band, until the BS allocates distributed channel resources to the UE. The UE may change its data transmission mode to distributed data transmission when it receives a distributed resource indicator.
The IEEE 802.16E specification describes a method for converting data transmission modes. If the maximum standard deviation for SNRs across all frequency bands in the time domain are relatively large and the mean SNR for the entire frequency band is greater than a threshold value, then the localized mode is appropriate for the UE. According to IEEE 802.16E, a UE moving at high speeds will have a time domain channel variance that is relatively large, while a UE moving at low speeds will have a time domain variance that is relatively small. Localized data transmission can be used for UEs moving slowly.
The uplink load for localized transmission is high, as more uplink signals are required to transmit CQI across several sub-bands. Localized data transfer cannot achieve much of a selective frequency gain in comparison to distributed data transport, as the SNRs for all sub-carriers is basically the same, regardless if they are distributed or localized data carriers. Their adaptive modulation gains are the same whether they use localized data transmission or distributed data transmission. Localized data transmission requires an uplink CQI for multi-bands. This means that it has a heavier signaling burden than distributed data transmission. Even for low-speed UEs that have a relatively high SNR on a flat fading channel with a low-speed fading channel, it is possible to achieve the same selective gain for distributed data transmission as localized data transmission. The distributed data transmission is therefore more appropriate.
Therefore, some improvements can be made to the IEEE 802.16E mode transition method to allow the UE to use a better transmission mode for transmitting data.
The present invention aims to create a measurement record for a transmission mode decision. A BS can use the measurement report to determine if a UE’s channel has a high frequency selectivity and then indicate the best mode for the UE based upon the result.
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