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Its granularity is 0. The RX baseband is operating in the baseband clock domain of MHz. The RX baseband block diagram is shown in Figure Blue arrows indicate the data path while yellow ones are connected to the control path. Details about the information are available in the following sections. The data source block selects the source for the receiver. The synchronization detects the packet start and compensates an estimated carrier frequency offset.
In parallel, the power measurement block calculates the received signal power. Then channel estimation, equalization, and phase tracking is done. The constellation with field assignment information is provided to the RX Bit Processing block.
Modeling and Performance of the IEEE 802.11p Broadcasting for Intra-Platoon Communication.
Inside this block the modulation is reversed, the bits are deinterleaved, decoded using a Viterbi core and descrambled. Every module is designed to keep up with the data rate from the upstream module, so there is no need for throttle control inside the modules. The timing of the transfers is described in the following sections. The power measurement module calculates the baseband signal power and the RF input power. The block diagram is shown in Figure Based on the incoming samples, x , the signal power, s , is calculated over a window of 64 samples as described in Equation 1.
The output of this calculation is updated after 64 samples arrive. The next step is the iterative calculation of the logarithm to the base of The value of s shifts n times to the left until the MSB contains a one. This value represents the baseband signal power in dBFS. Based on p , the RF input power r is calculated using the power calibration offset and the RF gain see Equation 2.
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Both values are given from the host. The analog gain value is subtracted from p because applying gain before ADC means that the RF input power is lower than the measured signal power. The power calibration offset is based on the calibration data of the device. This mapping is assumed to be linear at all gain levels. The value of r is compared against the given CCA energy threshold. If this threshold is exceeded, the CCA energy detect signal is asserted. The purpose of the synchronization module is to find the packet start in the continuous sample stream.
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The block diagram of the synchronization unit is shown in Figure 14 and details of data types, control information, and identifiers used in equations can be found in Table 5. In the baseband clock domain of MHz, approximately every third sample is valid. Each VI must use the enable chain to update only on valid samples.
The data rate is not changed by any VI. The synchronization block is implemented in two parallel paths refer to Figure 14 to minimize the latency on the data path. The upper path finds the packet start sample index and estimates the carrier frequency offset CFO based on the Schmidl and Cox algorithm . These estimates are used by the lower path, which is the main data path, to compensate CFO and generate the packet start pulse for downstream modules.
For testing purposes, there is a bypass for the synchronization block where the packet start index can be given from the host. This path is not included in Figure Use this bypass in combination with RX samples from the host or internal loopback to characterize the RX baseband without the impact of synchronization algorithms. As shown in Figure 14, the upper path of the synchronization block starts to calculate the autocorrelation of the received signal x see Equation 3. The normalized magnitude and the phase of the autocorrelation window, s , are given at the output of the autocorrelation module for each sample.
Under ideal conditions, this autocorrelation scheme results in a normalized magnitude equal to 1 as shown in Figure To find the transition from L-STF to L-LTF, a so-called synchronization timing metric is calculated based on the magnitude of the normalized autocorrelation, as shown in Equation 4. The ideal behavior of this timing metric, tm , is also shown in Figure Based on the indices of the minimum and maximum value of this metric and the distance between minimum and maximum, the sample index of the packet start is calculated using the following steps:.
Based on this algorithm and corresponding processing delays, the packet start sample index is calculated and given to the Frame Alignment module. During the calculation, the number of samples to cut into the OFDM guard interval is taken into account. In addition to timing estimation, the phase of the autocorrelation is averaged over CP values and used for CFO estimation. This CFO estimation is based on the phase output of the peak search. In the lower path of the synchronization block, the estimated CFO is compensated by applying a digital frequency shift.
The Frame Alignment module generates the packet start trigger pulse at the sample index given by the timing metric evaluation. After the synchronization has indicated a packet start signal, further triggering of packet start signals is blocked until the synchronization is rearmed by the PHY RX end indication , generated at the end of the packet.
This blocked status is indicated by the asserted CCA signal detect signal. The latencies for the different modules in the Synchronization block are illustrated in Figure The left part of the figure contains the modules of the upper path. The latency of those modules sum up to 68 clock cycles. Since the peak of the timing metric is located samples before L-LTF-2, the packet start index is calculated before the packet start signal is asserted and there is no effective delay.
The latency of the lower data path is shown in the right part of Figure This latency increases the length of the RX processing path by 15 clock cycles. Details of data types, control information, and identifiers used in equations are presented in Table 6. The Sample Timing Generation module gets samples from the Synchronization module along with the packet start index.
It starts passing samples to downstream modules as soon as the packet start signal is asserted. The control information is carried by the sample timing cluster, which contains the following elements:. The FFT starts execution as soon as samples are provided. During the execution, no samples are taken on the input. A FIFO is placed before the input to capture the samples that arrive in the meantime. On finishing execution, the subcarriers are provided at the output consecutively. The OFDM symbol index from the incoming sample timing cluster is passed through this module, parallel to the data stream.
The maximum gain of the FFT is if the energy is limited to only one subcarrier. Therefore, the fixed point data type is extended by nine bits to capture this output dynamic range of the FFT module. The Demapper block aligns two control information clusters with the data stream. The first cluster is the subcarrier timing cluster, which contains the following elements:. The frequency offset index is generated based on the control information from the RX PHY state machine refer to section 0. The second control information cluster is the field map. This cluster is made up of Booleans, and each Boolean represents one field of the Similar to a one—hot—code, only one of these Booleans is asserted for each sample.
The packet structure is known to the Demapper module. Downstream modules can take this field map to filter for specific fields, such as the pilot subcarriers. The inverse channel transfer function is calculated for each subcarrier R individually using the L-LTF definitions L from section The signal names are included in Figure The frequency offset index k from the subcarrier timing is used.
The channel estimation block is implemented in a parallel path to minimize latency to the data path. The values of H est are given to the channel equalization module where they are stored in memory. They have the same data type as the incoming subcarriers.
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Beginning with the L-SIG, the channel equalization uses those values to apply zero forcing to get signal Y est. Larger values are saturated. The signal Y est is passed to the pilot phase modules that follow the same structure as the channel estimation and equalization. Removing the cyclic prefix residual carrier frequency offset after the synchronization leads to a phase jump between consecutive OFDM symbols. These sequences are taken from Section This operation does not change the magnitude of the values, so the fixed point format is kept. A summary for all submodules is given in Table 7.
The Cyclic Prefix Removal module removes 64 samples from the stream. Because of the chosen FFT architecture configuration the output of the Xilinx core is given burstwise. This transfer timing is kept for all downstream modules. During the packet, the FFT executes and unloads samples in clock cycles after the last sample arrived. By the time the last sample is available on the input, the FIFO is empty, and it is passed to the core as fast as possible. All other modules have a fixed latency. The RX bit-processing chain deinterleaves, decodes, and descrambles the data. Details about data types and control information are given in Table 8.
The first module of the chain is the Packet Termination module. Passing only these samples ensures that the packet end is correctly processed. The next block is the Align Configuration module, which has two functions. All other control information is terminated in this module.
The bit-processing configuration is transferred parallel to the data stream, and it contains the following information:. The second function is the filtering of all noncoded fields for downstream modules. Based on the given modulation scheme, an array of up to eight softbits is given at the output.
The data type of each softbit is unsigned 8-bit integer.
The Softbit Serializer module takes this array of softbits and provides the serialized stream on the output. The number of valid softbits in the array is derived from the modulation. An internal FIFO is used to buffer softbits on the input. The Deinterleaver module reverts the BCC interleaver operations defined in section The write operation into the memory is based on equation of , which reverses the second permutation. The read operation is based on equation of , which reverses the first permutation.
Reading is started as soon as all softbits of the current OFDM symbol are saved to memory. A double page memory is used, which enables reading and writing at the same time. Based on Figure and of , the Depuncturer module converts the incoming bit stolen data sequence to the bit inserted data sequence. Each bit gets a puncturing flag attached depending on whether it was transmitted or left out. One element of A and the corresponding element of B are combined into an array of two elements, where A and B are as defined in Figure and of . The array is given to the Viterbi decoder, which is a wrapper for the Xilinx Viterbi core.
The block valid has the same latency as the data path. After the last softbit of the current code word, the Viterbi is flushed to get the remaining bits out of the core. On the output of the core, the block valid information can filter out the zeros from the flushing operation. The bits of the code word are provided at the output.
The Descrambler module processes the bits at the output of the decoder.
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If the scrambler is disabled, the input bits are bypassed to the output. On activation, detected by the rising edge of the enable signal, the Descrambler module assumes it is receiving a packet starting with the SERVICE field and uses the first seven bits to extract the scrambler seed.
Those initial bits are overwritten by zeros. Afterward, all bits are descrambled with the recovered seed until deactivation. The length of the PSDU is given by the configuration. Padding bits are removed. The output timing of the submodules is given in Table 9. The number of values depends on the format, bandwidth, and MCS. The referred variables can be found in Table , of  and Table , of .
In brackets, the minimum and maximum values are given indicating the valid range. The first module that changes this pattern is the Configuration Alignment. Only subcarriers belonging to coded fields remain on the output. Since there are multiple pilot tones, this stream contains gaps. The gaps are gone after the Deinterleaver module because the softbit stream is read burstwise from the internal memory. The Depuncturer adds gaps to this data stream when there are two valid bits of stream A and B available.
Adding punctured bits does not produce gaps. The Xilinx Viterbi core generates data on the output as soon as new bits are provided to the input. As a result, the output pattern is not changed. The masking of the PSDU reduces the data rate by factor 8. Most of the modules have a fixed latency. The delay of the Softbit Serializer depends on the modulation. For BPSK, each subcarrier is mapped to one softbit so the serialization does not add any delay. The internal FIFO is empty when the last value arrives. The FIFO delay is unknown. The latency is 2 because of internal registers.
For QAM, each softbit array has to be split into eight softbits on the output. The delay for the last softbit added with the two register stages results in clocks latency. The read operation starts as soon as the last value arrives. N CBPS softbits have to be read before the last sample is available on the output of the Deinterleaver. An additional latency of 11 is incurred because of the pipeline stages. The latency of the Viterbi decoder is determined by the Xilinx Viterbi decoder core. An additional latency of one is incurred due to one pipeline stage. The latency for other configurations can be calculated using Equation 7 with values from Table , of  or Table , of .
Notice that the synchronization is controlled indirectly by the state machine. The RX end indication is used to rearm the synchronization. The state diagram is given in Figure The word timing in this diagram refers to the timestamp when the last sample of the packet was received, which is included in the PHY RX end indication. This is the startup state. In this state, the internal configuration is reset such that it can receive the first coded field in the packet L-SIG in the primary subband. This setting consists of the The unknown length of the packet means that the last OFDM symbol index is set to the maximum unsigned bit integer value of 65, The L SIG check includes verifying the following conditions:.
The result of the check is used as condition L-SIG valid in the state machine. As soon as this condition is evaluated the state machine leaves this state. If L-SIG is invalid the reception of the current packet is aborted. The last OFDM symbol index is set to 0. Because there is no packet length information available at this point in time, the timing information is marked as invalid.
Furthermore the internal format violation flag is set. If a valid L-SIG was received, the next state depends on the packet format selected from the host. In the The index of the last OFDM symbol is calculated based on equation of . If the L-SIG was valid and the format is set to Only the index of the last OFDM symbol can be calculated, which also results in a known packet timing. The format still remains The Viterbi decoder flush required flag in the bit processing configuration cluster is set for the second OFDM symbol.
This bit-processing configuration cluster is aligned with the data stream in the RX Bit Processing block by the Align Configuration module see Section 3. Hence, accurate indication of the current OFDM symbol index is available from the RX Bit Processing module and can be used to set the Viterbi decoder flush required flag. This PSDU length is greater or equal to the exact payload size. This state can abort a running reception when an invalid signal field occurs.
The global timestamp is captured at this point in time to provide the end of the packet as the new frame timing. The PHY RX end indication is generated using the internal information about format violation and timing validity in addition to this new frame timing. This field is entered when the signaling information was correctly received and the data field is to be decoded. Furthermore, in For The valid bits limitation is not used in this case. The state is left after clock cycles, which is the duration of one OFDM symbol. This waiting period is required because either the RX IQ processing or RX bit processing chain or both could still be working on samples that must be terminated before setting the configuration for a new L-SIG reception.
Since the processing is based on OFDM symbol boundaries, after the duration of one symbol, all modules are in idle state. Time is represented on the horizontal axis. On the vertical axis, several selected modules with important outputs or that change the transfer timing are displayed. The colored rectangles correspond to the data values of one OFDM symbol. The size and the placement among the time axis are related to the latencies and transfer timings of the modules.
The arrows are based on the timing information. Neither the start nor the end position has to be related to the module that generates or consumes this control information. Figure 22 shows the timing of the receiver for an RF and Synchronization add the latency between over-the-air transmission and the synchronization output.
The decoding and flushing of the Viterbi decoder takes most of the time. This results in larger amount of bits on the Softbit Serializer module output. The Viterbi decoder keeps about bits stored due to the internal latency. All other DATA symbols are similar in timing. Due to padding bits, the decoding can end before the last bit has been received. After the Initialization state, the RX chain is ready to process a new packet. Figure 23 illustrates the termination of the reception in case L-SIG was not valid.
Once it is determined that L-SIG field contents are invalid, the last OFDM symbol index is set to zero, and the state machine goes to wait for last sample state shortened to wait in Figure During this time the FFT unloads the remaining data. The reception of an This information is not handled in RX Bit processing chain. This scenario results in a large number of bits generated by the LLR Demapper, which are serialized by the Softbit Serializer. Reading and writing the Deinterleaver memory overlaps for this large number of bits is the reason for having a double page memory in this module.
The MAC RX module performs frame validation, consisting of subframe detection for packets received in Subsequently MPDU type recognition is performed. For supported frame types, MAC header evaluation and address filtering is done. Finally MSDU extraction is performed by a configurable filter operation. All five submodules are described in more detail in the following sections. Refer to Section J. It checks the MPDU delimiter and provides the contained information to subsequent modules. For received packets in During the check, the 4 FCS bytes are removed. The module implements a small state machine to extract control information, such as the frame end timing validity and value, from the MPDU start indication primitive and the PHY RX end indication primitive.
This information is collected in the RX info indication and forwarded to the Channel State module. For supported frame types, MAC header evaluation is executed, including destination MAC address check for all frames or Source MAC address extraction for frames with address field 2, such as data frames. Currently supported frame types are Data and ACK.
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The filter also allows removal of MAC headers. The filtered received data and control information is converted into a serial data stream for transferring it using a target-to-host FIFO to the host. The default filter configuration for If you want to perform MAC operations on the host, the filter configuration has to be adapted. The TX baseband operates in the baseband clock domain of MHz.
Its block diagram is shown in Figure The data source block selects the source for the transmitter. The module furthermore applies channel duplication and rotation as needed for The modulated bits are then translated into the frequency domain using IFFT.
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The frames consist of a header and an optional body. The header generation modules utilize the frame configuration cluster, which contains all supported header fields. As the ACK carries no body, only the header must be serialized. For transmissions in Version 1. Furthermore, it ensures correct interframe spacing for the following scenarios:. All three modules are described in the following sections in more detail. The module Timing Control implements the actual generation of timing information timing signals for the transmission part. At startup, a regular slot timing pattern is generated.
The pattern consists of two signals, which are also shown in Figure The module Backoff performs the backoff procedure as defined in  Section 9. The backoff counter is initialized with the desired backoff value, provided through the TX after backoff request.
At the appropriate timing instant within relevant slots, which is indicated to the module with the slot M2 start signal, the CCA information is checked and if the channel is idle, the backoff counter is decremented. If the counter reaches zero, this condition is indicated via the signal backoff done to the module Data Pump. The module Data Pump coordinates the actual data transmission functionality. The module accepts requests for transmission with or without application of the Those requests are processed based on the timing and backoff information described earlier in the section.
The module also provides information about active transmissions to the Backoff module to ensure that this is taken into account during backoff counting. At a given instant of time, only one pending or active transmission request is allowed for transmission after backoff and one for transmission after SIFS. In addition the functions described previously, the module MAC TX also provides statistics information. The types of the data path and the elements of the control path are listed in Table Each signal field is generated in one burst. The next downstream module is the Bit Serializer module, which converts data fields and PSDU data into one bit per cycle.
A FIFO at module start ensures the module can process the incoming data rate. After bit serialization scrambling, convolutional encoding, puncturing, and interleaving are applied as described in In addition, existing MAC and PHY functions have been enhanced and obsolete features were removed or marked for removal.
Some clauses and annexes have been renumbered. Due to the favorable propagation characteristics of the low frequency spectra, The protocol intends consumption to be competitive with low power Bluetooth , at a much wider range. This extends some of the mechanisms in Currently in development, this project has the goal of providing 4x the throughput of By doing so, the interference between Clients is reduced, and the overall throughput is increased, since multiple Clients can receive data at the same time.
With With this technique, multiple Clients are assigned with different Resource Units in the available spectrum. In order to have enough amount of subcarriers to support the requirements of OFDMA , the number of subcarriers are increased by a factor of 4 compared to Since the available bandwidths have not changed and the number of subcarriers are increased with a factor of 4, the subcarrier spacing is reduced by a factor of 4 as well.
This introduces 4 times longer OFDM symbols. It is an amendment that defines a new physical layer for It will be an extension of the existing 11ad, aimed to extend the throughput, range and use-cases. The main use-cases include: indoor operation, out-door back-haul and short range communications.
The peak transmission rate of Across all variations of However, this does not apply to typical deployments in which data is being transferred between two endpoints, of which at least one is typically connected to a wired infrastructure and the other endpoint is connected to an infrastructure via a wireless link. This means that, typically, data frames pass an Due to the difference in the frame header lengths of these two media, the application's packet size determines the speed of the data transfer.
This means applications that use small packets e. Other factors that contribute to the overall application data rate are the speed with which the application transmits the packets i. The latter is determined by distance and by the configured output power of the communicating devices. The same references apply to the attached graphs that show measurements of UDP throughput.
Each represents an average UDP throughput please note that the error bars are there, but barely visible due to the small variation of 25 measurements. Markers for traffic profiles of common applications are included as well. These figures assume there are no packet errors, which if occurring will lower transmission rate further. These are commonly referred to as the "2. Each spectrum is sub-divided into channels with a center frequency and bandwidth, analogous to the way radio and TV broadcast bands are sub-divided.
The 2. The latter channels have additional restrictions or are unavailable for use in some regulatory domains. The channel numbering of the 5. These are discussed in greater detail on the list of WLAN channels. In addition to specifying the channel center frequency, One consequence is that stations can use only every fourth or fifth channel without overlap. Availability of channels is regulated by country, constrained in part by how each country allocates radio spectrum to various services. At one extreme, Japan permits the use of all 14 channels for Other countries such as Spain initially allowed only channels 10 and 11, and France allowed only 10, 11, 12, and 13; however, Europe now allow channels 1 through It is more correct to say that, given the separation between channels, the overlapping signal on any channel should be sufficiently attenuated to minimally interfere with a transmitter on any other channel.
Due to the near-far problem a transmitter can impact desense a receiver on a "non-overlapping" channel, but only if it is close to the victim receiver within a meter or operating above allowed power levels. Conversely, a sufficiently distant transmitter on an overlapping channel can have little to no significant effect. Confusion often arises over the amount of channel separation required between transmitting devices. This occasionally leads to the belief that four "non-overlapping" channels 1, 5, 9, and 13 exist under This does not mean that the technical overlap of the channels recommends the non-use of overlapping channels.
The amount of inter-channel interference seen on a configuration using channels 1, 5, 9, and 13 which is permitted in Europe, but not in North America is barely different from a three-channel configuration, but with an entire extra channel. However, overlap between channels with more narrow spacing e. IEEE uses the phrase regdomain to refer to a legal regulatory region. Different countries define different levels of allowable transmitter power, time that a channel can be occupied, and different available channels.
Most Wi-Fi certified devices default to regdomain 0, which means least common denominator settings, i. The regdomain setting is often made difficult or impossible to change so that the end users do not conflict with local regulatory agencies such as the United States ' Federal Communications Commission. The datagrams are called frames. Current Frames are divided into very specific and standardized sections. Some frames may not have a payload. The first two bytes of the MAC header form a frame control field specifying the form and function of the frame.
This frame control field is subdivided into the following sub-fields:. The next two bytes are reserved for the Duration ID field. An Each field can carry a MAC address. Address 1 is the receiver, Address 2 is the transmitter, Address 3 is used for filtering purposes by the receiver. The payload or frame body field is variable in size, from 0 to bytes plus any overhead from security encapsulation, and contains information from higher layers.
As frames are about to be sent, the FCS is calculated and appended. When a station receives a frame, it can calculate the FCS of the frame and compare it to the one received. If they match, it is assumed that the frame was not distorted during transmission.
Management frames are not always authenticated , and allow for the maintenance, or discontinuance, of communication. Some common The body of a management frame consists of frame-subtype-dependent fixed fields followed by a sequence of information elements IEs. Control frames facilitate in the exchange of data frames between stations. Data frames carry packets from web pages, files, etc. Similar to TCP congestion control on the internet, frame loss is built into the operation of To select the correct transmission speed or Modulation and Coding Scheme , a rate control algorithm may test different speeds.
The actual packet loss rate of an Access points vary widely for different link conditions. If the sender does not receive an Acknowledgement ACK frame, then it will be resent. Within the IEEE Both the terms "standard" and "amendment" are used when referring to the different variants of IEEE standards.
The standard is updated by means of amendments. Amendments are created by task groups TG. Both the task group and their finished document are denoted by Updating In order to create a new version, TGm combines the previous version of the standard and all published amendments. TGm also provides clarification and interpretation to industry on published documents. New versions of the IEEE Various terms in For example, Time Unit usually abbreviated TU is used to indicate a unit of time equal to microseconds.
Numerous time constants are defined in terms of TU rather than the nearly equal millisecond. Also the term "Portal" is used to describe an entity that is similar to an In , a group from the University of California, Berkeley presented a paper describing weaknesses in the In the attack, they were able to intercept transmissions and gain unauthorized access to wireless networks. The IEEE set up a dedicated task group to create a replacement security solution, These started to appear in products in mid In January , the IEEE set up yet another task group "w" to protect management and broadcast frames, which previously were sent unsecured.
Its standard was published in In December , a security flaw was revealed that affects some wireless routers with a specific implementation of the optional Wi-Fi Protected Setup WPS feature. While WPS is not a part of Many companies implement wireless networking equipment with non-IEEE standard These changes may lead to incompatibilities between these extensions.
From Wikipedia, the free encyclopedia. Main article: IEEE This section needs to be updated. Please update this article to reflect recent events or newly available information. June November March Main article: Archived from the original on Retrieved American Radio Relay League. The Verge. Official industry association web site. Archived from the original on September 3, Retrieved August 23, The New York Times. Lewis November 25, Wi-Fi Now.