It is assumed that a maximum of 4 users can be served by the SBS when the SF=4 or 8 users when the SF=8. Each user, k, is assigned a pseudo noise (PN) sequence of chips defined as: Nc (6.2) is the nth chip where elements of are +/- 1. Assuming the system is sampled at the chip rate, transmission is represented as: (6.3) where is the information bearing signal, lasting for chips. The signal in the presence of noise is ith received as: (6.4) where channel response. is the integer delay of user u and is additive noise. =user u’s Coherence Time The coherence time ( tells us tells us the time that the channel remains constant due to the effects of Doppler. Doppler frequency impacts at mmWave frequencies were shown as an important consideration to make (section 5.2.3). Assuming carrier frequencies of 28GHz and 72GHz with a maximum UE velocity in the small cell of 0.5km/h, coherence times of 77ms and 30ms respectively are given. This tells us that the channel will remain constant over the duration of many slot periods considering Figure 6.8 which may help to minimise the amount of CSI required. If the coherence time is limited the number of orthogonal pilot sequences that are assigned to cell is also limited. This can be a problem when considering LSAS schemes where neighbouring cells use the same carrier frequency and pilot symbols. In such cases pilot contamination can be a problem [160]. Channel Parameter Estimation Algorithm –Proposed Both proposed architectures will require estimation of CSI and significantly estimation of the multipath delay components. In both transmit and receive, data and pilot are separately BPSK modulated on the I and Q channel respectively, orthogonal variable spreading factor (OVSF) codes are suggested on the pilot and data to maintain orthogonality. Different users use different UL scrambling codes to create a unique traffic channel. Neglecting mutual interference between the data and pilots, the signal received at the base station can be separated into I and Q channels. The Q channel can be used to estimate the channel parameters.
It is assumed that a maximum of 4 users can be served by the SBS when the SF=4 or 8 users when the SF=8. Each user, k, is assigned a pseudo noise (PN) sequence of Nc chips defined as: (6.2) is the nth chip where elements of are +/- 1. Assuming the system is sampled at the chip rate, transmission is represented as: (6.3) where is the ith information bearing signal, lasting for chips. The signal in the presence of noise is received as: (6.4) where =user u’s channel response. is the integer delay of user u and is additive noise. Coherence Time The coherence time ( tells us tells us the time that the channel remains constant due to the effects of Doppler. Doppler frequency impacts at mmWave frequencies were shown as an important consideration to make (section 5.2.3). Assuming carrier frequencies of 28GHz and 72GHz with a maximum UE velocity in the small cell of 0.5km/h, coherence times of 77ms and 30ms respectively are given. This tells us that the channel will remain constant over the duration of many slot periods considering Figure 6.8 which may help to minimise the amount of CSI required. If the coherence time is limited the number of orthogonal pilot sequences that are assigned to cell is also limited. This can be a problem when considering LSAS schemes where neighbouring cells use the same carrier frequency and pilot symbols. In such cases pilot contamination can be a problem [160]. Channel Parameter Estimation –Proposed Algorithm Both proposed architectures will require estimation of CSI and significantly estimation of the multipath delay components. In both transmit and receive, data and pilot are separately BPSK modulated on the I and Q channel respectively, orthogonal variable spreading factor (OVSF) codes are suggested on the pilot and data to maintain orthogonality. Different users use different UL scrambling codes to create a unique traffic channel. Neglecting mutual interference between the data and pilots, the signal received at the base station can be separated into I and Q channels. The Q channel can be used to estimate the channel parameters.
PhDThesisWithCorrections.docx