The cellular land mobile radio system is designed to support high teletraffic capacity and transmission quality, even in urban environments with abundant obstructions. The transmission environment is challenging due to excessive propagation loss and heavy multipath, which vary and fluctuate as mobile users move. The system's architecture and signal design aim to mitigate these impairments. Simple statistical models are insufficient for describing the spatial-time variations of the channel, and physically-based canonical propagation models are essential for understanding the interaction process. 1. **Excessive Loss**: Mobiles must be serviced within cells, but line-of-sight between the cell-site antenna and the mobile is often obstructed. In highly populated areas, structures and objects can obstruct the transmission path, and excess loss is used to achieve required isolation from other cells. 2. **Scattering and Reflections**: Propagation within congested cells is dominated by scattering and reflections from surrounding structures and objects. Omnidirectional antennas are used to collect signals from all directions, and multipath scatter from nearby objects or reflected from large surfaces can significantly impact signal quality. 3. **Fading Channel**: Multipath formed by scatterers and reflectors results in coherent wave-interference patterns, causing signal strength peaks and dips, known as fading. 1. **Path-loss**: This describes the propagation of total power, including direct and forward scattered contributions, with slow phase changes. Path-loss changes slowly with frequency and is influenced by geometrical spreading, near grazing propagation, and shadowing. 2. **Channel Quality**: Multipath propagation creates "flat fading" for narrow-band receivers and "delay spread" or "Doppler spread" for broadband receivers. These variations are frequency, time, and space-dependent and are mitigated by signal processing techniques.The cellular land mobile radio system is designed to support high teletraffic capacity and transmission quality, even in urban environments with abundant obstructions. The transmission environment is challenging due to excessive propagation loss and heavy multipath, which vary and fluctuate as mobile users move. The system's architecture and signal design aim to mitigate these impairments. Simple statistical models are insufficient for describing the spatial-time variations of the channel, and physically-based canonical propagation models are essential for understanding the interaction process. 1. **Excessive Loss**: Mobiles must be serviced within cells, but line-of-sight between the cell-site antenna and the mobile is often obstructed. In highly populated areas, structures and objects can obstruct the transmission path, and excess loss is used to achieve required isolation from other cells. 2. **Scattering and Reflections**: Propagation within congested cells is dominated by scattering and reflections from surrounding structures and objects. Omnidirectional antennas are used to collect signals from all directions, and multipath scatter from nearby objects or reflected from large surfaces can significantly impact signal quality. 3. **Fading Channel**: Multipath formed by scatterers and reflectors results in coherent wave-interference patterns, causing signal strength peaks and dips, known as fading. 1. **Path-loss**: This describes the propagation of total power, including direct and forward scattered contributions, with slow phase changes. Path-loss changes slowly with frequency and is influenced by geometrical spreading, near grazing propagation, and shadowing. 2. **Channel Quality**: Multipath propagation creates "flat fading" for narrow-band receivers and "delay spread" or "Doppler spread" for broadband receivers. These variations are frequency, time, and space-dependent and are mitigated by signal processing techniques.