tailieunhanh - Vehicular Technologies Increasing Connectivity Part 14

Tham khảo tài liệu 'vehicular technologies increasing connectivity part 14', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Propagation Aspects in Vehicular Networks 381 where h t Ti aki exp j2nfd cosdk t ộkd 3 k 0 and TO h t T h t Ti 6 T - Ti 4 i 0 with akd and ộk i being the amplitude and phase of the i-th contribution that arrives to the receiver with an angle 0k j with respect to the direction of motion and delay Ti. The term fd is the maximum Doppler frequency also called Doppler shift . fd v Ac where v refers to the receiver velocity Ac c0 fc is the wavelength associated to the carrier frequency fc and c0 is the speed of light. The 6 function is the Dirac delta and 8 denotes convolution. Eq. 4 corresponds to the time-variant impulse response of the wireless radio channel. Specifically h t t is the response of the lowpass equivalent channel at time t to a unit impulse generated T seconds in the pass Parsons 2000 . h t T is known as the input delay-spread function and is one of the four system functions described by Bello Bello 1963 which can be used to fully characterize linear time-variant LTV radio channels. The term hit Ti is the time-dependent complex coefficient associated to a delay Ti and can be expressed as h t Ti hiR t jhiQ t 5 where hiR t aki cos 2nfd cosdk t ộk 6 k 0 and hiQ t aki sin 2n fd cosOkdt ộkd 7 k 0 are the in-phase and quadrature components respectively. In practice many physical channels can be considered stationary over short periods of time or equivalently over small spatial distances due to the transmitter receiver or interacting objects displacement. Although these channels may not be necessarily stationary in a strict sense they usually are considered wide sense stationary WSS channels. Also a channel can exhibit uncorrelated scattering US in the time variable . contributions with different delays are uncorrelated. The combination of the WSS and US assumptions yields the WSSUS assumption which has been very used in channel modeling for cellular systems. Under the WSSUS assumption the channel can be represented as a tapped delay line TDL where the .