IEEE 802.15.4 PHY Layer

 

Property Range

 

Raw Data Rate 868 MHz:20 Kb/s;

915 MHz:40 Kb/s;

2.4 GHz: 250 Kb/s

Range 10-20 m
Latency Down to 15ms
Channels

 

868/915 MHz: 11 Channels, 2.4 GHz: 16 Channels
Frequency Band Two PHYs: 868 MHz/915 MHz and 2.4 GHz
Addressing Short 8-bit or 64-bit IEEE
Channel Access CSMA-CA and slotted CSMA-CA
Temperature Industrial temperature range -40 to +85 C

 

The Physical (PHY) layer is concerned with the interface to the physical transmission medium (radio, in this case), exchanging data bits with this medium as well as with the layer above (the MAC sub layer). More specifically, its responsibilities towards the physical radio medium include:

1. Channel assessment

2. Bit level communications (bit modulation, bit demodulation, packet synchronization)

The PHY layer also offers the following services to the MAC sub layer:

PHY Data Service: Provides a mechanism for passing data to and from the MAC sub layer.PHY Management Services: Provides mechanisms to control radio communication settings and functionality from the MAC sub layer.

PHY functionalities:

1) Activation and deactivation of the radio transceiver

2) Energy detection within the current channel

3) Link quality indication for received packets

4) Clear channel assessment for CSMA/CA

5) Channel frequency selection

6) Data transmission and reception

The operating frequency bands are depicted in the figure below.

channel-structure
The standard specifies two PHYs:
1) 868 MHz/915 MHz direct sequence spread spectrum (DSSS) PHY (11 channels)
    1 channel (20Kb/s) in European 868MHz band
    10 channels (40Kb/s) in 915 (902-928) MHz ISM band
2) 2450 MHz direct sequence spread spectrum (DSSS) PHY (16 channels)
    16 channels (250Kb/s) in 2.4GHz band
    2.4 GHz PHY can be used to attain higher throughput and lower latency / lower duty cycle.
phy-layer

PHY packet fields:

1) Preamble (32 bits) – synchronization

2) Start of packet delimiter (8 bits) – shall be formatted as “11100101”

3) PHY header (8 bits) – PSDU length

4) PSDU (0 to 127 bytes) – data field

The packet structure of the IEEE 802.15.4 PHY layer is depicted in Figure above. The first field of this structure contains a 32-bit preamble. This field is used for symbol synchronization. The next field represents the start of a packet delimiter. This field of 8 bits is used for frame synchronization. The 8-bit PHY header field specifies the length of the PHY service data unit (PSDU). The PSDU field can carry up to 127 bytes of data.

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IEEE 802.15.4: CASE STUDY

The main design objective of the IEEE 802.15.4 open standard is to support the wireless connectivity of a vast number of industrial, home, and medical applications, including automotive monitoring and control, home automation, ubiquitous and pervasive health care, gaming, connecting devices to a PC, and sensor rich environments.

Such applications require a small, low cost, highly reliable technology that offers long battery life, measured in months or even years, and automatic or semiautomatic installation. The IEEE 802.15.4 standard supports these requirements by trading off higher speed and performance for architectures that benefit from low power consumption and low cost.

Most of these applications require only low to medium bit rates (up to some few hundreds of kbps), moderate average delays without too stringent delay guarantees, and for certain nodes it is highly desirable to reduce the energy consumption to a minimum. The physical layer offers bit rates of 20 kbps (a single channel in the frequency range 868 –868.6 MHz), 40 kbps (ten channels in the range between 905 and 928 MHz) and 250 kbps (16 channels in the 2.4 GHz ISM band between 2.4 and 2.485 GHz with 5-MHz spacing between the center frequencies). There are a total of 27 channels available, but the MAC protocol uses only one of these channels at a time; it is not a multi channel protocol.

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How to get free Jio 4G SIM for any 4G phone with Preview Offer (unlimited calls, data & SMS)

Reliance after providing free Jio 4G SIM offer for bunch of smartphones, now started offering the same to the all 4g smartphone users in India. As we all know, the Reliance Jio SIM offer includes unlimited data, voice calls, video calls, and SMS for 90 days from the day of activation of your Jio SIM.

There are many other smartphone users in India who wanted to enjoy this offer, but doesn’t know how to apply for free Reliance Jio 4G SIM card. We currently have some 4g Smartphone devices and have successfully got a free Jio SIM card. So here is a step-by-step guide that will guide you to grab the offer.

Screenshot_2016-09-01-16-11-03_com.android.chrome_1472726783827

First you need to download and install the My Jio App from Google Play Store. You can check here for the app link.

Once the app is successfully installed, launch it from the app drawer. Now you will list of 10 more apps from the My Jio app main screen. You need to install all those applications one after another from Play Store or else tap “Install Jio apps” located at the top of the screen to install all Jio apps in just single click.

After installing all the Jio apps, you need to wait for few minutes and then reboot your device. Once the device boots-up, disable Wi-Fi connectivity and enable Mobile-Data.

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Launch “MyJio” app and then tap on My Jio section. Here you will find the option “Get Jio SIM”, tap the same to continue. In the next screen you will see 5 different steps to be followed which helps to generate the preview code, documents to be submitted, find the nearest store, activate your Jio SIM, and finally avail your Jio offer.

Screenshot_2016-09-01-16-11-23_com.android.chrome_1472726803694

Once everything done, you need to visit nearest gio store with required documents to get a free SIM card. After receiving it, you need to wait 24 hours for SIM activation. Make sure the Jio SIM is inserted in SIM 1 slot to enjoy unlimited features like calling, 4G data and SMS for a period of 90 days

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