1. EEE440 Modern Communication Systems Wireless and Mobile Communications

2. Indoor Propagation Propagation impairments in an indoor radio channel are caused mainly by: –reflection from, and diffraction around, objects (including walls and floors) within the rooms; –transmission loss through walls, floors and other obstacles; –channelling of energy, especially in corridors at high frequencies; –motion of persons and objects in the room, including possibly one or both ends of the radio link,

3. Indoor wireless propagation Like the outdoor propagation, the indoor propagation also experience multipath dispersion caused by a large number of reflectors and scatterers In a typical indoor environment, a fixed antenna (usually ceiling-mounted) serves a number of mobile radios In narrow-band, multipath causes fluctuations in the received signal envelope and phase There are critical differences from the outdoor The outdoor channel is stationary in time and nonstationary in space. Signal dispersion is mainly caused by large fixed objects. Because the base antenna is elevated and mobile antenna are at relatively low level, the effects of people and moving vehicle are negligible. The indoor channel is neither stationary in space nor in time The motion of people and equipments with a low-level ceiling mounted antenna is not negligible

4. Indoor wireless propagation The indoor channel has higher path losses and sharper changes in the mean signal level compared to the outdoor channel Applicability of a simple negative exponent distance-dependent path loss model is not universally accepted for indoor. Rapid motion and high velocities are absent. The Doppler shift is negligible

5. Indoor wireless propagation Maximum delay of multipath signals is typically less than one microsecond Delay spread is usually less than 100 nanoseconds Frequency selective fading occurs at higher bandwidth

6. Modelling indoor wireless propagation Modelling indoor wireless propagation is highly complex For the multipath dispersion, a simple geometrical model is used The signal reaches the mobile via one or more main waves These main waves consist of a LOS ray and several rays reflected or scattered by main structures such as outer walls, floors, ceilings etc

7. Modelling indoor wireless propagation The resulting paths for each main wave arrive with very close delays, experience about the same attenuation, but have different phase values due to different path lengths There are three types of variations in the channel –Small-scale, midscale and large-scale variations Small-scale variations-Within a site the channel is quite similar since the channel structure does not change considerably over short distance. This is equivalent to the correlated fading in the outdoor channel within a short distance. Midscale-in local areas with similar antenna separation, there may be great differences in signal levels equivalent to shadowing in the outdoor Large-scale – the channel structure change drastically due to increase in the number of objects. Equivalent to path loss in the outdoor. But cannot be modeled simply by the same outdoor model.

8. Modelling indoor wireless propagation The impulse response approach can be used to characterise the channel For each point in the 3-dimensional space the channel is a linear time-varying filter with the impulse response given by

9. Modelling indoor wireless propagation In reality a mobile phone moving through the indoor channel experinces a space-varying fading phenomenon, so the impulse response varies at different points

10. Modelling indoor wireless propagation The number of multipath components, N in each impulse response is a random variable The mean value of N differs for different types of building The path variable sequences are random sequences and depend on the shape, size and construction of the building. The arrival times can be modelled by the modified Poisson distribution.

11. Modelling indoor wireless propagation Distribution of the pulse amplitudes –The difference in time delay of a number of paths is much less than the reciprocal of the transmission bandwidth and the paths cannot be resolved as distinct pulses –The unresolvable pulses add up and the envelope of their sum is observed –The envelope is a random variable

12. Modelling indoor wireless propagation The amplitude fading may follow different distribution depending on the conditions Various distribution have been reported: Rayleigh, Rician, Nakagami, Weibull, Lognormal, Suzuki

13. Modelling indoor wireless propagation The distribution of the arrival time –The Standard Poisson distribution cannot be used because indoor scatterers are not located with total randomness –The modified Poisson distribution has better fit –Other distribution may also apply depending on conditions

14. Modelling indoor wireless propagation The distribution of the path phases –No empirical model for path phases because of difficulties to measure the phase of individual multipath components –Uniform distribution is used –The signal phase is critically sensitive to path length As the path length changes by a wavelength (eg. 30cm at 1gHz), the phase changes by 2pi. Moderate changes in the position of the mobile result in great phase difference

15. Indoor wireless propagation Interdependencies within path variables Adjacent multipath components of the same impulse response profile are likely to be correlated because a number of scattering objects that produce them may be the same Correlation between the arrival times is due to the grouping property of local structures. The amplitude sequence is correlated with the arrival time sequence because later paths of a profile experience higher attenuation due to greater path lengths and possibly multiple reflections.

16. Indoor wireless propagation Temporal variations of the channel –Due to motion of people and equipments, the channel statistics changes even when the transmitter and receiver are fixed –Motion can introduce deep fade (sometimes as high as 20dB) –Different magnitude and duration of fade for different kind of buildings. Large-scale path losses –Greater than outdoor –Large variation can occur over very small distance –Complicated. Cannot use the conventional path loss model –No single model is appropriate for all conditions

17. Indoor wireless propagation Delay spread –Depends on size and types of buildings, existence of a clear LOS, room sizes, antenna separation –Determines whether frequency selective fading occurs or not –Generally less than the outdoor so can use higher bitrate Penetration Loss –Power lost as signal enters the buildings varies depending on types of building materials and various other factors –The difference between the received signal inside a building and around the parameter of that building –Important for frequency reuse –Depends on the construction materials, building orientation with respect to transmitter, internal layout etc.