X-MobilityTM, a set of the most advanced patents aiming at mobile wireless networking, utilizes RDW’s exclusive Mobile WiMAX + Wi-Fi IC, MIMOBand to achieve seamless multimedia over mobile wireless broadband.
X-MobilityTM contains advanced technologies including: Multi In Multi Out (MIMO), Enhanced Forward Error Correction (FEC) that utilize Convolution Turbo Coding (CTC) with HARQ to generate major improvements in packet error rate (PER), and Advanced Channel/Doppler tracking for fast fading channel. In a fast-speed wireless mobile networking environment, wireless channel is usually modeled as fast fading channel in which channel response is time variant. Due to the large fluctuation in amplitude and phase in fast fading channel, the pilot in frequency domain could be completely corrupted after FFT demodulation which makes the channel estimation in frequency domain is very undesirable. Then for high speed case, RDW introduces a hybrid time-frequency domain channel estimation scheme, which decreased the amplitude and phase fluctuate before FFT demodulator and greatly enhance the system performance in very fast fading case.
Doppler Effect is another serious impairment introduced by high moving speed. When a wave source and a receiver are moving relative to one another, the frequency of the received signal will not be the same as the source. When they are moving toward each other, the frequency of the received signal is higher then the source, and when they are approaching each other, the frequency decreases. This is called the Doppler Effect. An example of this is the change of pitch in a car’s horn as it approaches then passes by. This effect becomes important when developing mobile radio systems. Doppler shift can cause significant problem in WiMAX because OFDM is sensitive to carrier frequency offsets.
X-MobilityTM targets mobile networking issues involving:
-
Advanced Channel/Doppler Tracking
Utilizing the information of pilots in each symbol, X-MobilityTM isolates Doppler shift with multi-path channel fading and track them respectively. It uses an efficient two dimensional interpolation to estimate the fast fading channel. This unique technique can achieve very accurate channel estimation with extremely high speed.
-
Diversity with MIMO
Utilizing multiple antennas, wireless system may obtain several independent observations of the signal. Spatial diversity can be achieved by combining these independent observations together. X-MobilityTM provides a novel way to fully use the information from each observation, which can combat multipath fading efficiently.
-
Turbo Code with HARQ
In wireless environment, a robust FEC is very necessary to enable reliable communications. Fully utilizing the recurring property of Turbo code, X-MobilityTM integrates Turbo Code with HARQ to achieve high performance. With X-MobilityTM’s unique design, Turbo code and HARQ can be implemented in a very efficient way without any sacrifice of performance.
-
Performance-Oriented Power Management
Power consumption is a very critical criterion for mobile station (MS) receiver design in a WiMAX system. The object of X-Mobility™ technology offers high quality mobile communication service while consuming as little energy as possible. The key idea in reducing the power consumption in MS is to distinguish the quality of signals and adjust power management parameters. The parameters will control the power supply subsystem, such as switching regulator to downgrade the power level while still meet the system performance requirements. Analogically, it is like using more strength to lift heavier things while use less strength to lift the lighter things while obtaining future knowledge of weight.