Embedded WiFi technology in the medical monitoring of programmes

Currently, IEEE802.11 wireless local area network standard in voice communication, wireless, Office, etc are widely used, but mainly limited to PCs, laptops, and other common platform of wireless communication.

Wireless LAN in the electronics, industrial control, mobile handheld devices such as embedded application requirements in your environment. How do I in embedded system integration of WLAN broadband communication, become embedded system applications in a hotspot.

1 IEEE802.11 wireless LAN IEEE802.11b series including IEEE802.11, IEEE802.11a, IEEE802.1lb, IEEE802.1lg four standards.

This stage of the product more IEEE802.11b. This article is targeted at IEEE802.1lb standard, describes an implementation of embedded WiFi.

IEEE802.11b standard is in IEEE802.11 developed on the basis of the work in 2.4 GHz band, using CCK modulation technology, the highest transfer rates up to 11 Mbps, with deployment easy, reliable communication, strong anti-interference ability, low cost, flexibility, and portability, high throughput, and other characteristics.

It allows wireless users can get the Ethernet level of network performance, speed and availability, and can be seamlessly integrated in a variety of LAN technologies will produce a maximum meet user demand network. WiFi is the abbreviation of Wireless Fidelity, IEEE802.11b wireless standards exclusively. In introducing the work mode IEEE802.11b, first describes the basic concepts.

1.1 IEEE802.11b basic concepts

STA is the access portion of the wireless media, often called the network adapter or network interface card.

STA can be mobile or fixed. Each STA support authentication (authentication), authentication (deauthentication), encryption and data transfer, etc.

Basic service set BSS (Basic Service Set) is the basic form IEEES02.11b LAN, basic service set cell can contain multiple STA.

BSS basic service set has a coverage. In the coverage of basic service set STA can maintain mutual communication, each BSS has a basic service set identification number BSSID.

Independent basic service set IBSS (Independent BSS) is the most basic type of LAN IEEE802.11b, a minimum of IEEE802.11b LAN can only contain two STA.

In this mode, the STA to direct traffic. Because this type of IEEES02.11b LAN usually necessary arrangements so that the network mode is commonly referred to as ad hoc (Latin, translated as "ad hoc") mode. Site (STA) and basic service set (BSS) relate is dynamic, STA free to power on, power off, enter or leave the BSS coverage.

DSS (Distribution System Service) used to connect multiple BSS.

Due to the physical layer coverage limits determines can support of STA and direct communication between STA. To solve this problem, the introduction of DS (Distribution System), it can take multiple BSS constitute an extension of the network.

Access Point AP is short for General translation of "wireless access node" or "bridge".

Mainly in the media access control layer MAC play wireless workstation and wired local area network of bridges.

ESS (Extended Service Set), DS and multiple BSS allows IEEE802.11 constitute an arbitrary size and complexity of wireless network.

IEEE802.11b put such a network is called extended service set network. Similarly, the ESS also has an identifying name, i.e. the ESSID. 1.2 IEEE802.11b work patterns

IEEE 802.1lb has two working mode: Ad-hoe and Infra-structure model.

IEEE standard in stand-alone basic service set (IBSS) to define Ad-hoc mode of client-side collection, to basic service set (BSS) to Infrastructure mode defined by the client-side collection.

In Ad-hoc mode, the client cannot directly and the network of other client communications.

Ad-hoc mode is designed so that in the same spectrum coverage of customers can communicate with each other. If an Ad-hoc network mode customers want and the network of customer communications, the network must have a customer gateway, and performs routing functionality.

In Infrastructure mode, every customer will have their communication message to forward all communications AP.AP message.

These messages can be sent to Ethernet, can also be sent to the wireless network. This is an integrated Ethernet and wireless network infrastructure for application mode. Wireless access node is responsible for the management and roaming, and other bands command work. An AP connectsto 1024 site.

2 the design of embedded WiFi

Embedded WiFi structure and standard PC/OS platform.

To common microprocessor/microcontroller on WiFi communication, its hardware structure, software level must be reduced. The following spoke: Prism MAC instructions embedded WiFI design for software and hardware.

2.1 embedded WiFi hardware design

Embedded environment WiFi hardware interface as shown in Figure 1.

Compared with standard platforms, no PCMCIA Bridge. Figure 1 is an embedded environment PC2MCIA interface card and bus connections open MCU.

Since MAC including Memory space Prism and I/O memory two space, so you will need two films selected by or door control read and write space of choice.

PCMCIA package Prism MAC 26 root address line driver Prism MAC only needs to address lines A0 to A9, other address all grounding line. For bus not open processor, you can use the I/O port line simulation approach to reading and writing.

2.2 embedded WiFi software design

In Linux, WinCE, operating environments, you can use the manufacturers to provide the device driver to use the WiFi card.

This system is generally on hardware resources (such as CPU performance, storage capacity, etc) have higher requirements. For many embedded applications, due to a hardware resource limitations, many systems are simple OS (such as uC/0S etc) or no 0S environment running, then you need the entire software protocol for appropriate reductions.

TCP/IP protocol implementations in many articles have been more telling.

Here the main Prism MAC, for example, introduce infinite network drivers, namely embedded WiFi drivers.

Prism MAC provides consumers with a set of interface registers, registers, and through these Prism MAC for communication.

These registers is located on the Attribute Memory [2] space, you can use the direct access Memory address AttribLlte. Table 1 lists the commonly used registers PRISM MAC and its definition.

In order to read and write these registers, defines two functions: unsigned int getReg (unsigned int reg) and void selReg (unsigned int int val reg, usnigned).

Prism MAC drive is to command registers a command to manipulate MAC. Frequently used commands are allocated buffer, query the network card status, initialize the card, read data, write data, etc.

Prism MAC driver needs to provide for the upper MAC read and write functions, and some control function, the implementation of the function prototype is as follows:

void init_mac(void) void reset_mac(void) WORD wc_write(WORD*buff，WORD len) WORDwc_read(WORD*buff，WORDmaxlen) B00L get_wlan(void)

Reset_mac (void) is used to start the system or the system needs to be reset, reset Prism MAC while driving the use of a variable is initialized.

Inh_mac (void) function finishes initializing network controller and firmware to the NIC controller application for the use of the buffer required for the preservation of the RID. Wc_write (W0RD * burf, W0RD len) function in the buff len bytes written to the send buffer, MAC, and then write send command to send the command registers the network card, the function returns the actual length of data sent. Wc_read (WORD * buff, WoRD maxlen) function receives the input data. Returns the actual length of the data received, on the upper-layer protocols, call wc_read, can the data in the buff do protocol analysis. For TCP/IP, actually removed may be IP, ARP, and other types of messages. Get_wlan (void) by accessing EvStat register determine whether data is received, returns to judge the results. If so, you have the income to PrismMAC data frames share the data area. This function simply PrismMAC data frame first read out the fairly so Ethernet frame's header. Readout of data format for upper-layer protocols call get_wlan later, if the return value is TRUE, you can access the destination address, source address, the frame type and other variables to determine whether processing the data received. If you need to receive data, you can call the wc — read to read the data.

3 embedded WiFi in the application of medical care

Embedded WiFi in many areas have a wide range of applications.

Here is a concrete implementation of embedded WiFi — mobile monitoring systems. The monitoring system for hospital patient care, the use of embedded WiFi technology, available in a mobile environment, to be logging objects for digit grouping, real-time monitoring.

3.1 hardware structure

Mobile monitoring system consists of a server and multiple mobile intensive care unit.

Server-side include 1 PC or laptop, one wireless AP and 1 alarm, hardware structure and connections are relatively simple, in this no longer description.

Mobile monitors hardware structure including power supply module, pressure sensor, acceleration sensor module and a wireless network card modules.

Mobile monitors using Ti's ultra low-power microcontroller MSP430F148 as CPU.

Acceleration sensor module using the AD company's accelerometer ADXL202 for acceleration test, or gravity acceleration measurement, analysis, i.e. for patient tilt down test. Pressure sensor with MotorOla medical dedicated MPX2300DT, has good features and low voltage operation for linear output pulse measurement.

Power use 3.6 V battery-powered, after simple voltage transformation to satisfy the power requirements of mobile intensive care unit.

Wireless network cards using IntersilPrism2 PCMCIA network card chip set. It is a IEEE802.11b compliant network adapter. 3.2 software structure

Ad-hoc mode, move the monitors and the distance between servers is very short.

In order to increase the monitoring range, the mobile Telemonitoring system work in Infrastructure mode, the server-side AP and mobile monitors are equivalent to an STA, mobile monitors and servers can be in different BSS. Mobile monitors, AP's BSS together constitute an ESS, use DSS communication.

Server-side software module is used primarily to received from the network to the data in separating out the tilt, mobile monitors configuration information, pulse, and according to the information to the police, to move the monitors control.

Mobile monitors major complete Acceleration (tilt) data acquisition, pulse signal acquisition, data transceiver, sensor and stopping control.

The software can be divided into two levels: the application tier and the driver layer. Shadows for hardware drivers, driver layer above is the application layer.

Mobile monitoring systems with embedded WiFi technology, supports digital grouping, you can group objects to be logging detection, real-time data transmission at the same time; guarantee the reliability and accuracy of monitoring, in actual use has very good results.