Wireless Physical layer
This page covers wireless physical layer basics and provides links to various wireless physical layer standards which include WLAN-11a, 11b, 11n, WiMAX-Fixed(OFDM-16d), mobile(OFDMA-16e), GSM, GPRS, CDMA, TD-SCDMA, LTE, WirelessHART physical layers and more.
Physical layer as per OSI terminology refers to any medium which carry information either in analog or in digital form.
The medium can be copper wire, twisted shielded cable or air.
Wireless physical layer refers to the layer which protects data to reach reliably from transmitter to the receiver
in the presence of noisy channel environment. The channel incorporates various impairments which include fading,awgn,phase noise,
frequency offset and so on.
Hence the role of wireless physical layer is to incorporate
features which facilitates data to be retrived from the corrupted received packet/frame.
The most common functions of Wireless Physical layer are outlined below with block schematic.
• It provides modulation-demodulation functionalities at transmit and receive end of the wireless chain.
• It provides Forward Error Correction functionality at receiver by incorporating Convolution encoder and viterbi decoder at transmit and receive end respectively. Other forward error correction techniques such as reed solomon, turbo coding, LDPC are also employed based on channel and BER requirement of the system.
• It incorporates interleaver and deinterleaver at transmit and receive end to help recover data in case of selective fading conditions.
• It incorporate scrambler and descrambler at transmit and receive end to help distribute energy across larger band and avoid any
adjacent channel interference.
The figure describes the basic wireless physical layer modules and their order. Initially data is fed to the randmomizer which randomizes the binary data and removed long stream of zeros or ones and hence help spread the power across the larger bandwidth as mentioned and also help in clock synchronization at the receiver. Refer scrambler circuit with matlab code.
The next module in the chain helps in error correction at the receiver by incorporating redundancy at the transmit side. This enhances bit error rate of the system at the same SNR compare to non-FEC systems. Refer convolution encoder which is used most commonly as FEC encoder in wireless physical layer. Viterbi decoder is used at the receiver as FEC decoder.
The third most important block which makes transmit data reach in the small and large scale fading environment is interleaver. It does permutation of the contiguous subcarriers and hence continuguous data from FEC encoder will be mapped on distributed subcarriers. The permutation equation is known to the deinterleaver module in the receiver and hence help depermute the received sequence. Refer Interleaver equation with matlab code to understand the concept of interleaving.
The interleaved data is fed as input the data mapping or data modulation. There are various types of modulation. The most common type used in next generation wireless standards is digital modulation. The modulation techniques employed typically are BPSK,QPSK and QAM. Refer what is modulation page to know more about the modulation.
After the modulation, baseband data is processed through DAC and passed to the RF stage. In RF part up conversion is done to the transmit frequency and amplified before coupled with the antenna. Similarly in the receiver, data is passed through preamplifier(mostly Low noise amplifier) and downconverted before being passed to the ADC. output of the ADC is given to reverse modules of one used in the transmit end.
Wireless Physical layer standards
Following are some of the useful links for various wireless physical later standards designed to meet
different data rate,coverage and wireless channel requirements.
It covers physical layer standards such as WLAN-11a,11b,11n,11ac,WiMAX-Fixed(OFDM),mobile(OFDMA),GSM,GPRS,CDMA,TD-SCDMA,LTE,WirelessHART and more.
• Zigbee PHY Layer
• Bluetooth PHY
• Zwave PHY Layer
• 11a physical layer
• LTE Physical layer
• fixed wimax physical layer-OFDM
• 11n physical layer
• wirelessHART physical layer
• Physical layer measurements
• 11b physical layer
• Mobile wimax Physical layer-OFDMA
• GSM Physical layer
• GPRS physical layer
• CDMA physical layer
• TD-SCDMA Physical layer
• WCDMA Physical layer
• WCDMA TDD vs FDD physical layer
• WLAN 11ac physical layer
• 10,40,100 Gigabit Ethernet Physical layer
• WLAN 802.11ad Physical layer
Useful Links
forward error correction
Turbo encoder
BER
channel model
OSI and TCPIP basics