Ieee802.15.4 Mac Library
This example shows how to simulate the IEEE® 802.15.4™ asynchronous CSMA MAC [ 1 ] using the Communications Toolbox™ Library for the ZigBee® Protocol.
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- IEEE 802.15.4 ZigBee Transceiver. Contribute to bastibl/gr-ieee802-15-4 development by creating an account on GitHub.
2017-11-8 Product data sheet Rev. 3.0 — 7 November 2017 4 of 100 NXP Semiconductors JN517x IEEE802.15.4 Wireless Microcontroller with a protocol stack library. 4.2 CPU and memory An ARM Cortex-M3 CPU allows software to be run on-chip, its processing power being shared between the IEEE802.15.4 MAC protocol, other higher layer protocols and the user. Background The IEEE 802.15.4 standard specifies the PHY and MAC layers of Low-Rate Wireless Personal Area Networks (LR-WPANs) 1.The IEEE 802.15.4 PHY and MAC layers provide the basis of other higher-layer standards, such as ZigBee, WirelessHart®, 6LoWPAN and MiWi., WirelessHart®, 6LoWPAN and MiWi.
Background
The IEEE 802.15.4 standard specifies the MAC and PHY layers of Low-Rate Wireless Personal Area Networks (LR-WPANs) [ 1 ]. The IEEE 802.15.4 MAC and PHY layers provide the basis of other higher-layer standards, such as ZigBee, WirelessHart®, 6LoWPAN and MiWi. Such standards find application in home automation and sensor networking and are highly relevant to the Internet of Things (IoT) trend.
The IEEE 802.15.4 MAC [ 1 ] specifies two-basic MAC modes: (i) non-beacon-enabled, and (ii) beacon-enabled MAC. The non-beacon enabled MAC is an asynchronous CSMA (Carrier-sense Multiple Access) MAC, which is very similar to the IEEE 802.11 MAC. The beacon-enabled MAC allows two different MAC periods: (i) a synchronized-CSMA MAC period, and (ii) a time-slotted, contention-free MAC period. This example provides an extensive simulation of the non-beacon-enabled, asynchronous, CSMA-based IEEE 802.15.4 MAC.
Network Setup
An IEEE 802.15.4 PAN (personal area network) is set up by a standard process between end devices and PAN coordinators. First, devices that would like to join a network perform either active or passive scanning. Active scanning means that a device first transmits a Beacon Request and later on it performs passive scanning. Passive scanning means that the device sniffs to collect beacon frames from PAN coordinators (who may have received their Beacon Request in the case of active scanning). Upon the collection of beacons during passive scanning, the end device chooses the PAN with which it would like to associate. Then it transmits an Association Request to the coordinator of this PAN and the coordinator acknowledges it.
In contrast to IEEE 802.11, the coordinator does not follow the acknowledgment of an Association Request with an immediate transmission of an Association Response. Instead, the IEEE 802.15.4 coordinator first stores the Association Response locally; it is only transmitted when the end device sends a Data Request and the coordinator acknowledges it. The IEEE 802.15.4 standard uses the term indirect transmission to refer to this mechanism for transmitting frames. In general, this mechanism is very useful for battery-powered devices of low-traffic networks (e.g., sensor networks). Such devices may periodically activate their radios to check whether any frames are pending for them, instead of continuously using their radios to receive a frame immediately.
Once the Association response is received and acknowledged, the end device is associated with the PAN. At that time, data frames can be exchanged between the coordinator and the end device in any direction. The data frames may be acknowledged, depending on their 'Acknowledgment Request' indication.
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Asynchronous Medium-Access Control (MAC)
The asynchronous CSMA IEEE 802.15.4 MAC is similar to the generic CSMA operation and the IEEE 802.11 MAC. In this MAC scheme, acknowledgment frames are transmitted immediately, without using the CSMA method. All other frames are transmitted using CSMA.
Specifically, once a device has a frame to transmit, it randomly chooses a backoff delay (number of backoff periods) from the range [0 2^BE-1], where BE is the backoff exponent. The duration of each backoff period is 20 symbols. For the OQPSK PHY in 2.4 GHz, this duration corresponds to 128 chips and 0.32 ms. Once the device has waited for the chosen number of backoff periods, it performs carrier sensing. If the medium is idle, the device begins transmission of its frame, until it is entirely transmitted.
If the medium is busy during carrier sense, then the backoff exponent increments by 1 and a new number of backoff periods is selected from the new [0 2^BE-1] range. When the backoff counter expires again, carrier sensing is performed. If the maximum number of backoff countdowns is reached without the medium being idle during any carrier sensing instance, then the device terminates its attempts to transmit the frame.
Network Simulation Capabilities
This example offers an implementation for the described network setup process and the CSMA method via the lrwpan.MACFullFunctionDevice and the lrwpan.MACReducedFunctionDevice classes. Specifically, the following capabilities are enabled:
Active and passive scanning
Association Request and Association Response exchange
Indirect transmissions using Data Requests
Frame acknowledgments and frame retransmissions if acknowledgments are not timely received
Short and long interframe spacing (SIFS and LIFS)
Network Simulation
802.15.4g
In this section, we create an IEEE 802.15.4 network of 3 nodes: one PAN coordinator and two end devices. The network simulator is configured to process all devices at increments of a single backoff duration (20 symbols, 0.32 ms).
First, the following code illustrates the association of the first device with the network.
Once the 1st end device has been associated, data frames are randomly injected into the link between the end device and the PAN Coordinator.
Next, a third device joins the PAN and data frames are subsequently exchanged between the coordinator and both end devices, in a star topology fashion (end devices must only transmit frames to coordinators). In this case, the output is suppressed.
More nodes can be added to the network, as long as the channel relationship is established accordingly (i.e., the received signals as a function of the transmitted signals).
Further Exploration
You can further explore the following generator and decoding functions, as well as the configuration object:
Selected Bibliography
Ieee 802 15 4 Mac Library Application
IEEE 802.15.4-2011 - IEEE Standard for Local and metropolitan area networks--Part 15.4: Low-Rate Wireless Personal Area Networks (LR-WPANs)
This example shows how to generate waveforms, decode waveforms and compute BER curves for different PHY specifications of the IEEE® 802.15.4™ standard [ 1], using the Communications Toolbox™ Library for the ZigBee® Protocol.
Background
The IEEE 802.15.4 standard specifies the PHY and MAC layers of Low-Rate Wireless Personal Area Networks (LR-WPANs) [ 1 ]. The IEEE 802.15.4 PHY and MAC layers provide the basis of other higher-layer standards, such as ZigBee, WirelessHart®, 6LoWPAN and MiWi. Such standards find application in home automation and sensor networking and are highly relevant to the Internet of Things (IoT) trend.
Physical Layer Implementations of IEEE 802.15.4
The original IEEE 802.15.4 standard and its amendments specify multiple PHY layers, which use different modulation schemes and support different data rates. These physical layers were devised for specific frequency bands and, to a certain extent, for specific countries. This example provides functions that generate and decode waveforms for the physical layers proposed in the original IEEE 802.15.4 specification (OQPSK in 2.4 GHz, BPSK in 868/915 MHz), IEEE 802.15.4b (OQPSK and ASK in 868/915 MHz), IEEE 802.15.4c (OQPSK in 780 MHz) and IEEE 802.15.4d (GFSK and BPSK in 950 MHz).
These physical layers specify a format for the PHY protocol data unit (PPDU) that includes a preamble, a start-of-frame delimiter (SFD), and the length and contents of the MAC protocol data unit (MPDU). The preamble and SFD are used for frame-level synchronization. In the following description, the term symbol denotes the integer index of a chip sequence (as per the IEEE 802.15.4 standard), not a modulation symbol (i.e., a complex number).
OQPSK PHY: All OQPSK PHYs map every 4 PPDU bits to one symbol. The 2.4 GHz OQPSK PHY spreads each symbol to a 32-chip sequence, while the other OQPSK PHYs spread it to a 16-chip sequence. Then, the chip sequences are OQPSK modulated and passed to a half-sine pulse shaping filter (or a normal raised cosine filter, in the 780 MHz band). For a detailed description, see Clause 10 in [ 1 ].
BPSK PHY: The BPSK PHY differentially encodes the PPDU bits. Each resulting bit is spread to a 15-chip sequence. Then, the chip sequences are BPSK modulated and passed to a normal raised cosine filter. For a detailed description, see Clause 11 in [ 1 ].
ASK PHY: The ASK PHY uses BPSK modulation for the preamble and the SFD only. The remaining PPDU bits, i.e., the PHY header (PHR) and the MPDU, are first mapped to 20-bit symbols in the 868 MHz band and to 5-bit symbols in the 915 MHz band. Each symbol is spread to a 32-chip sequence using a technique known as Parallel Sequence Spread Spectrum (PSSS) or Orthogonal Code Division Multiplexing (OCDM). The chip sequence is then ASK modulated and passed to a root raised cosine filter. For a detailed description, see Clause 12 in [ 1 ].
Lr Wpan
GFSK PHY: The GFSK PHY first whitens the PPDU bits using modulo-2 addition with a PN9 sequence. The whitened bits are then GFSK modulated. For a detailed description, see Clause 15 in [ 1 ].
802.15.4 Pdf
Waveform Generation, Decoding and BER Curve Calculation
This code illustrates how to use the waveform generation and decoding functions for different frequency bands and compares the corresponding BER curves.
Further Exploration
You can further explore the following generator and decoding functions:
lrwpan.PHYGeneratorOQPSK, lrwpan.PHYDecoderOQPSKNoSync and lrwpan.PHYDecoderOQPSK
lrwpan.PHYGeneratorBPSK and lrwpan.PHYDecoderBPSK
lrwpan.PHYGeneratorASK and lrwpan.PHYDecoderASK
lrwpan.PHYGeneratorGFSK and lrwpan.PHYDecoderGFSK
802.15.4 Wifi
Selected Bibliography
IEEE 802.15.4-2011 - IEEE Standard for Local and metropolitan area networks--Part 15.4: Low-Rate Wireless Personal Area Networks (LR-WPANs)