<body ng-app="app">

    <div ng-controller='controller'>

        <ng-form name="formName">

            <input type="text" ng-model="val1" required/>

            <div ng-show="myForm.items" ng-repeat="item in myForm.items">

                <label>

                    <input type="checkbox" name="group[]" ng-model="$parent.selectedValue[item.id]" value="{{item.id}}" ng-required="!someSelected($parent.selectedValue)" />{{item.sId}}</label>

            </div>{{selectedValue}}

            <input type="submit" ng-disabled="formName.$invalid">

                {{formName.$invalid}}

        </ng-form >

    </div>

</body>

app = angular.module('app', []);

app.controller('controller', function ($scope) {

    $scope.myForm = {};

    $scope.selectedValue = {};

    $scope.myForm.items = [{

        id: 1,

        sId: "analog"

    }, {

        id: 2,

        sId: "isdn"

    }, {

        id: 3,

        sId: "dsl"

    }];

    $scope.someSelected = function (obj) {

        console.log('some selecgted');

        var rs=Object.keys(obj).some(function (key) {

            return obj[key];

        });

        console.log(rs);

        return rs;

    }

    $scope.submitForm = function(){

        $scope.clickSubmit = 'clickSubmit';

    }

});